Podcast
Questions and Answers
Grey matter consists of nerve cell bodies and neuroglia.
Grey matter consists of nerve cell bodies and neuroglia.
True
White matter is located on the outer layer of the brain.
White matter is located on the outer layer of the brain.
False
The central nervous system includes the cerebrum and spinal cord.
The central nervous system includes the cerebrum and spinal cord.
True
CSF is produced at a rate of 100 ml per day.
CSF is produced at a rate of 100 ml per day.
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The fourth ventricle is located between the cerebellum and brainstem.
The fourth ventricle is located between the cerebellum and brainstem.
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Ependyma lines the ventricles in the brain.
Ependyma lines the ventricles in the brain.
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The choroid plexus is responsible for producing grey matter.
The choroid plexus is responsible for producing grey matter.
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Neurons are excitable nerve cells.
Neurons are excitable nerve cells.
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The dura mater is the innermost layer of the meninges.
The dura mater is the innermost layer of the meninges.
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The pia mater is firmly attached to the brain.
The pia mater is firmly attached to the brain.
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Arachnoid mater is a vascular layer.
Arachnoid mater is a vascular layer.
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Dural partitions help to subdivide the cranial cavity.
Dural partitions help to subdivide the cranial cavity.
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The arachnoid granulations allow for the flow of blood into the arachnoid mater.
The arachnoid granulations allow for the flow of blood into the arachnoid mater.
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The meningeal dural layer encloses both the brain and the spinal cord.
The meningeal dural layer encloses both the brain and the spinal cord.
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The outer endosteal layer of the dura mater is tightly attached to the skull.
The outer endosteal layer of the dura mater is tightly attached to the skull.
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Dural sinuses are structures that contain arteries.
Dural sinuses are structures that contain arteries.
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A spinal tap should be performed at the L4/L5 level.
A spinal tap should be performed at the L4/L5 level.
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The spinal cord continues down to the L5 level.
The spinal cord continues down to the L5 level.
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The cranial nerve that is responsible for smell is CNII.
The cranial nerve that is responsible for smell is CNII.
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There are 31 pairs of spinal nerves in the human body.
There are 31 pairs of spinal nerves in the human body.
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The sympathetic nervous system is associated with 'rest and digest' functions.
The sympathetic nervous system is associated with 'rest and digest' functions.
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The trigeminal nerve is responsible for facial sensation and mandibular movements.
The trigeminal nerve is responsible for facial sensation and mandibular movements.
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Cervical nerves control the perineum and lower limbs.
Cervical nerves control the perineum and lower limbs.
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The oculomotor nerve is involved in eye movements.
The oculomotor nerve is involved in eye movements.
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Oligodendrocytes produce myelin in the central nervous system (CNS).
Oligodendrocytes produce myelin in the central nervous system (CNS).
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Astrocytes are responsible for producing the cerebrospinal fluid (CSF).
Astrocytes are responsible for producing the cerebrospinal fluid (CSF).
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Microglia act as specialized macrophages that remove damaged neurons.
Microglia act as specialized macrophages that remove damaged neurons.
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Schwann cells are found in the central nervous system (CNS).
Schwann cells are found in the central nervous system (CNS).
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There are 12 pairs of spinal nerves in the body.
There are 12 pairs of spinal nerves in the body.
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The central nervous system consists of the brain and spinal cord.
The central nervous system consists of the brain and spinal cord.
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The cerebrum has two separate hemispheres connected by the corpus callosum.
The cerebrum has two separate hemispheres connected by the corpus callosum.
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Satellite cells provide structural support in the central nervous system (CNS).
Satellite cells provide structural support in the central nervous system (CNS).
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Gyri are the depressions on the surface of the cerebrum.
Gyri are the depressions on the surface of the cerebrum.
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Ependymal cells form the epithelial lining of the ventricles in the brain.
Ependymal cells form the epithelial lining of the ventricles in the brain.
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CSF is produced primarily in the lateral ventricles.
CSF is produced primarily in the lateral ventricles.
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CSF flows through the interventricular foramen to the second ventricle directly.
CSF flows through the interventricular foramen to the second ventricle directly.
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CSF courses through the midbrain and subarachnoid space via the foramen of Magendie.
CSF courses through the midbrain and subarachnoid space via the foramen of Magendie.
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The arachnoid granulations are responsible for producing CSF.
The arachnoid granulations are responsible for producing CSF.
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The brain and spinal cord are protected by the skull and covered by the meninges.
The brain and spinal cord are protected by the skull and covered by the meninges.
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The cerebrospinal fluid is found in the endosteal layer of the dura mater.
The cerebrospinal fluid is found in the endosteal layer of the dura mater.
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CSF flows through the cerebral aqueduct to reach the fourth ventricle.
CSF flows through the cerebral aqueduct to reach the fourth ventricle.
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CSF is reabsorbed into the arterial circulation through the arachnoid granulations.
CSF is reabsorbed into the arterial circulation through the arachnoid granulations.
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Unipolar neurons have multiple neurites that extend from the cell body.
Unipolar neurons have multiple neurites that extend from the cell body.
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Bipolar neurons have two separate processes that arise from opposite ends of the cell body.
Bipolar neurons have two separate processes that arise from opposite ends of the cell body.
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The central nervous system consists of neurons and glial cells only.
The central nervous system consists of neurons and glial cells only.
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Dendrites are processes that carry impulses away from the cell body.
Dendrites are processes that carry impulses away from the cell body.
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Multipolar neurons have a single long axon and multiple dendrites.
Multipolar neurons have a single long axon and multiple dendrites.
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Neurons are not excitable cells and do not transmit nerve impulses.
Neurons are not excitable cells and do not transmit nerve impulses.
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The dorsal root ganglion contains unipolar neurons.
The dorsal root ganglion contains unipolar neurons.
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The central nervous system includes the spinal cord but not the brain.
The central nervous system includes the spinal cord but not the brain.
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The dura mater is the outermost layer of the meninges.
The dura mater is the outermost layer of the meninges.
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The arachnoid mater is a vascular layer that nourishes the brain.
The arachnoid mater is a vascular layer that nourishes the brain.
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Dural sinuses are structures that primarily contain venous blood.
Dural sinuses are structures that primarily contain venous blood.
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The subdural space is located between the arachnoid mater and the pia mater.
The subdural space is located between the arachnoid mater and the pia mater.
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The pia mater is a layer that ends at the level of S2.
The pia mater is a layer that ends at the level of S2.
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Arachnoid granulations allow for the flow of cerebrospinal fluid into the venous sinuses.
Arachnoid granulations allow for the flow of cerebrospinal fluid into the venous sinuses.
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Falx cerebri is a dural partition that projects into the cranial cavity.
Falx cerebri is a dural partition that projects into the cranial cavity.
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The meningeal layer of the dura mater is tightly attached to the vault of the skull.
The meningeal layer of the dura mater is tightly attached to the vault of the skull.
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A spinal tap should be performed at the L3/L4 level.
A spinal tap should be performed at the L3/L4 level.
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The sympathetic nervous system is responsible for 'rest and digest' functions.
The sympathetic nervous system is responsible for 'rest and digest' functions.
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There are 8 cervical nerves in the human body.
There are 8 cervical nerves in the human body.
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The trigeminal nerve is responsible for facial expression.
The trigeminal nerve is responsible for facial expression.
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A dermatome is a group of muscles innervated by motor nerve fibers from a specific spinal nerve.
A dermatome is a group of muscles innervated by motor nerve fibers from a specific spinal nerve.
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The subarachnoid space is where cerebrospinal fluid (CSF) is located.
The subarachnoid space is where cerebrospinal fluid (CSF) is located.
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Lumbar disc herniation can cause referred pain down the leg along the distribution of the sacral nerve.
Lumbar disc herniation can cause referred pain down the leg along the distribution of the sacral nerve.
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The glossopharyngeal nerve is responsible for vision.
The glossopharyngeal nerve is responsible for vision.
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The automatic, involuntary response to a stimulus in the nervous system is known as a reflex.
The automatic, involuntary response to a stimulus in the nervous system is known as a reflex.
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The lumbar nerves control the perineum and lower limbs.
The lumbar nerves control the perineum and lower limbs.
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The cerebrum is composed of a single hemisphere.
The cerebrum is composed of a single hemisphere.
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Polysynaptic reflexes involve a single synapse between the sensory neuron and the motor neuron.
Polysynaptic reflexes involve a single synapse between the sensory neuron and the motor neuron.
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The posterior part of the anulus fibrosus can rupture during a herniated intervertebral disc injury.
The posterior part of the anulus fibrosus can rupture during a herniated intervertebral disc injury.
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Presynaptic parasympathetic nerve cell bodies are located in the gray matter of the brainstem and the thoracic segments of the spinal cord.
Presynaptic parasympathetic nerve cell bodies are located in the gray matter of the brainstem and the thoracic segments of the spinal cord.
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Sensory ganglia are primarily found in the spinal cord and are responsible for autonomic functions.
Sensory ganglia are primarily found in the spinal cord and are responsible for autonomic functions.
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Visceral sensations can be imperceptible and generally originate from internal organs.
Visceral sensations can be imperceptible and generally originate from internal organs.
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The sympathetic chain is a correct term for pre-aortic ganglia located around the main abdominal arteries.
The sympathetic chain is a correct term for pre-aortic ganglia located around the main abdominal arteries.
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Afferent impulses carry information away from the central nervous system.
Afferent impulses carry information away from the central nervous system.
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The ventral horn of the spinal cord is larger in the cervical and lumbar regions due to a greater volume of tissue supplied.
The ventral horn of the spinal cord is larger in the cervical and lumbar regions due to a greater volume of tissue supplied.
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Autonomic ganglia are found along cranial nerves III, V, VII, and X, among others.
Autonomic ganglia are found along cranial nerves III, V, VII, and X, among others.
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Motor impulses are under voluntary control when they pertain to skeletal muscles.
Motor impulses are under voluntary control when they pertain to skeletal muscles.
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The sympathetic nervous system is known for its 'rest and digest' functions.
The sympathetic nervous system is known for its 'rest and digest' functions.
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The dura mater is the outermost layer of the meninges.
The dura mater is the outermost layer of the meninges.
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The facial nerve is responsible for hearing and balance.
The facial nerve is responsible for hearing and balance.
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Cervical spinal nerves are associated with the arms and neck.
Cervical spinal nerves are associated with the arms and neck.
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The arachnoid mater is primarily responsible for producing cerebrospinal fluid (CSF).
The arachnoid mater is primarily responsible for producing cerebrospinal fluid (CSF).
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A spinal tap is typically performed at the L5/S1 level to avoid damaging the spinal cord.
A spinal tap is typically performed at the L5/S1 level to avoid damaging the spinal cord.
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The pia mater is loosely attached to the brain.
The pia mater is loosely attached to the brain.
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There are 12 pairs of cranial nerves in the human body.
There are 12 pairs of cranial nerves in the human body.
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Dural sinuses are structures that contain venous blood.
Dural sinuses are structures that contain venous blood.
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The olfactory nerve is identified as CNIII.
The olfactory nerve is identified as CNIII.
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The falx cerebri separates the two hemispheres of the brain.
The falx cerebri separates the two hemispheres of the brain.
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Areolar tissue with internal vertebral venous plexus is one of the structures encountered before entering the subarachnoid space.
Areolar tissue with internal vertebral venous plexus is one of the structures encountered before entering the subarachnoid space.
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The arachnoid granulations facilitate the flow of cerebrospinal fluid into the bloodstream.
The arachnoid granulations facilitate the flow of cerebrospinal fluid into the bloodstream.
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The trigeminal nerve (CN V) is solely responsible for mandibular movements.
The trigeminal nerve (CN V) is solely responsible for mandibular movements.
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The endosteal layer of the dura mater is closely associated with the arachnoid mater.
The endosteal layer of the dura mater is closely associated with the arachnoid mater.
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Cerebrospinal fluid is absorbed from the subarachnoid space into the dural sinuses through the arachnoid granulations.
Cerebrospinal fluid is absorbed from the subarachnoid space into the dural sinuses through the arachnoid granulations.
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A dermatome refers to a specific collection of muscles innervated by motor nerve fibers from a particular cranial nerve.
A dermatome refers to a specific collection of muscles innervated by motor nerve fibers from a particular cranial nerve.
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The presence of sciatica is indicative of lumbar disc herniation involving L4 and L5 spinal nerves.
The presence of sciatica is indicative of lumbar disc herniation involving L4 and L5 spinal nerves.
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Polysynaptic reflexes involve only one synapse in the nervous system pathway.
Polysynaptic reflexes involve only one synapse in the nervous system pathway.
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The nucleus pulposus is located in the central region of the intervertebral disc and can be forced out during a herniation.
The nucleus pulposus is located in the central region of the intervertebral disc and can be forced out during a herniation.
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The only stimulus that can initiate a reflex response is a voluntary action.
The only stimulus that can initiate a reflex response is a voluntary action.
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Presynaptic parasympathetic nerve cell bodies are primarily located in the gray matter of the sacral segments S1-S5.
Presynaptic parasympathetic nerve cell bodies are primarily located in the gray matter of the sacral segments S1-S5.
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Visceral sensation generally originates from internal organs and is often perceptible only during disease.
Visceral sensation generally originates from internal organs and is often perceptible only during disease.
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Posterior root ganglia are primarily involved in motor functions and are located close to the ventral root of each spinal nerve.
Posterior root ganglia are primarily involved in motor functions and are located close to the ventral root of each spinal nerve.
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The sympathetic nervous system primarily controls voluntary motor impulses.
The sympathetic nervous system primarily controls voluntary motor impulses.
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The lateral horn of the spinal cord is present from T1 to L2 and S2 to S4 segments.
The lateral horn of the spinal cord is present from T1 to L2 and S2 to S4 segments.
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Sensory ganglia of cranial nerves are positioned along cranial nerves I, II, and III.
Sensory ganglia of cranial nerves are positioned along cranial nerves I, II, and III.
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Afferent impulses carry signals away from the CNS, while efferent impulses carry signals towards the CNS.
Afferent impulses carry signals away from the CNS, while efferent impulses carry signals towards the CNS.
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Ganglia located around the main abdominal arteries are classified as prevertebral ganglia.
Ganglia located around the main abdominal arteries are classified as prevertebral ganglia.
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The posterior ramus solely innervates the muscles of the anterior trunk.
The posterior ramus solely innervates the muscles of the anterior trunk.
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The ventral ramus does not innervate the limbs.
The ventral ramus does not innervate the limbs.
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Grey rami communicantes are responsible for transmitting signals from the spinal cord to the peripheral nervous system.
Grey rami communicantes are responsible for transmitting signals from the spinal cord to the peripheral nervous system.
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The anterior ramus includes branches that innervate intercostal nerves.
The anterior ramus includes branches that innervate intercostal nerves.
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The lateral cutaneous branch arises from the anterior ramus.
The lateral cutaneous branch arises from the anterior ramus.
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Study Notes
Neuroglia
- Non-excitable cells that provide structural support and produce myelin
- In the Central Nervous System (CNS), there are four types of neuroglia:
- Astrocytes: provide structural support, insulate synapses, uptake and synthesize neurotransmitters
- Oligodendrocytes: produce myelin
- Microglia: specialized macrophages that remove damaged neurons and infections
- Ependymal cells: form the epithelial lining of the ventricles in the brain and the central canal of the spinal cord, produce cerebrospinal fluid (CSF)
- In the Peripheral Nervous System (PNS), there are two types of neuroglia:
- Schwann cells: produce myelin
- Satellite cells: provide nutritional support and help regulate ion concentration
Synapses
- Neurons communicate with one another at synapses
- Pre-synaptic neuron: neuron conducting the impulse
- Post-synaptic neuron: neuron receiving the impulse
General Organization of the Nervous System
-
Functionally:
- Somatic: controls voluntary movements and reflexes
- Visceral (Autonomic Nervous System): controls involuntary functions of smooth muscle, cardiac muscle, and glands
-
Structurally:
-
Central Nervous System (CNS):
- Brain: located within the skull
- Spinal Cord: located within the vertebral canal
-
Peripheral Nervous System (PNS):
- Cranial Nerves: originate from the brain
- Spinal Nerves: originate from the spinal cord
-
Central Nervous System (CNS):
Major Divisions of the CNS
-
Forebrain:
- Cerebrum (Telencephalon): responsible for higher-level cognitive functions, including language, memory, and reasoning
- Diencephalon: responsible for regulating homeostasis, sensory relay, and emotional responses
- Midbrain (Mesencephalon): responsible for auditory and visual reflexes
-
Brainstem:
- Cerebellum (Metencephalon): responsible for coordinating movement, balance, and posture
- Pons (Metencephalon): responsible for relaying signals between the cerebrum and cerebellum, and regulating breathing
- Medulla Oblongata (Myelencephalon): responsible for regulating vital functions such as breathing, heart rate, and blood pressure
- Spinal Cord: responsible for relaying signals between the brain and the body, and controlling reflexes
Major Divisions of the PNS
- 31 pairs of spinal nerves: connect the spinal cord to the body
- 12 pairs of cranial nerves: connect the brain to the body
CNS - Cerebrum
- Surface: Gyri (elevations), Sulci (depressions), Fissures (deep depressions)
- Five lobes: frontal, parietal, temporal, occipital, insula
- Two separate hemispheres (by the longitudinal fissure) and connected by the corpus callosum
-
Grey matter: contains nerve cell bodies and neuroglia, located:
- In the cortex
- Scattered in the core (basal ganglia)
-
White matter: contains nerve fibers and neuroglia, located:
- Central/inner matter
Ventricles
- CSF-filled cavities:
- Two lateral ventricles
- One third-ventricle between the thalamic walls
- One fourth-ventricle between the cerebellum and brainstem
- Lined by ependyma
- CSF is produced at the rate of 500ml/day
CSF Flow
-
- CSF produced by the choroid plexus (mainly in the lateral ventricles)
-
- CSF flows through interventricular foramen to the third ventricle
-
- CSF flows through the cerebral aqueduct to the fourth ventricle
-
- CSF courses through the midbrain and subarachnoid space via the lateral foramina of Luschka and midline foramen of Magendie
-
- CSF gets reabsorbed into the venous circulation through the arachnoid granulations
Meninges
- Brain and spinal cord are protected by the skull and covered by the meninges
- Three layers:
-
Dura Mater: tough outer layer, composed of two layers
- Outer endosteal layer: attached to the skull
- Inner meningeal layer: forms dural partitions and sinuses
- Arachnoid Mater: delicate, spidery layer, separated from dura mater by subdural space, contains arachnoid granulations that allow CSF to flow into the bloodstream
- Pia Mater: inner layer, firmly attached to the brain and spinal cord
-
Dura Mater: tough outer layer, composed of two layers
Dural Partitions and Sinuses
- Dural partitions project into the cranial cavity and partially subdivide it, examples:
- Falx cerebri: separates the two cerebral hemispheres
- Falx cerebelli: separates the two cerebellar hemispheres
- Dural sinuses are intracranial venous structures where blood drains from the brain
Arachnoid Granulations
- Small finger-like projections of arachnoid mater that project into the dural venous sinuses allowing for one-way flow of CSF from the subarachnoid space into the bloodstream
Spinal Tap
- Should be performed at the level of L3/L4 or L4/L5 due to the termination of the spinal cord at this level, allowing for needle access to the subarachnoid space for CSF collection
Major Divisions of the PNS
- Somatic: controls voluntary movements and reflexes, including both sensory and motor components
-
Visceral (Autonomic Nervous System): controls involuntary functions of smooth muscle, cardiac muscle, and glands, including both sensory and motor components
- Sympathetic: "fight or flight" response
- Parasympathetic: "rest and digest" response
PNS - Cranial Nerves
- CNI - Olfactory: smell
- CNII - Optic: vision
- CNIII (Oculomotor), IV (Trochlear), VI (Abducent): eye movements
- CNV - Trigeminal: facial and scalp sensation, mandibular movements
- CNVII - Facial: facial expression
- CNVIII - Vestibulocochlear: hearing, balance
- CNIX (Glossopharyngeal), X (Vagus): swallowing, phonation
- CNXI (Accessory): neck and head movements
- CNXII (Hypoglossal): tongue movements
PNS - Spinal Nerves
-
31 pairs of spinal nerves:
- 8 Cervical: neck and upper limb
- 12 Thoracic: upper limb and thorax
- 5 Lumbar: abdomen and lower limb
- 5 Sacral: lower limb and perineum
- 1 Coccygeal: tailbone
- Contain a mixture of both sensory and motor fibers
Introduction to the Nervous System
- The nervous system is responsible for communication throughout the body.
- The nervous system carries signals from the brain to target tissues and organs.
- The nervous system has two parts: the central nervous system and the peripheral nervous system.
### Cellular Components of the Nervous System
- The basic unit of the nervous system is the neuron.
- Neurons are a type of excitable cells responsible for receiving and transmitting nerve impulses.
- Neurons vary in shape and size.
- Neurons can be found in the brain, spinal cord, and ganglia.
- Neurons have a cell body, dendrites, and an axon.
- The cell body contains the nucleus and is responsible for the neuron's metabolic activity.
- Dendrites are branching projections that receive information from other neurons and conduct it towards the cell body.
- Axons are long, slender projections that conduct nerve impulses away from the cell body.
Types of Neurons
- Unipolar neurons have a single neurite that divides a short distance from the cell body.
- Bipolar neurons have a cell body with two processes: one axon and one dendrite.
- Multipolar neurons have a cell body with numerous processes, including a long axon and multiple dendrites.
### Central Nervous System (CNS) Coverings
- The brain and spinal cord are covered by three layers of membranes called meninges.
- The dura mater is the outermost, thickest layer of the meninges.
- It has an outer endosteal layer and an inner meningeal layer.
- The arachnoid mater is a delicate, web-like layer located between the dura mater and pia mater.
- The pia mater is the innermost layer that is closely attached to the brain and spinal cord.
- The space between the arachnoid mater and pia mater is called the subarachnoid space and contains cerebrospinal fluid (CSF).
Dural Partitions
- The dura mater forms several partitions that divide the cranial cavity.
- The falx cerebri separates the two cerebral hemispheres.
- The falx cerebelli separates the cerebellar hemispheres.
###Arachnoid Granulations
- Arachnoid granulations are finger-like projections of the arachnoid mater that project into the dural venous sinuses.
- They allow CSF to flow from the subarachnoid space into the bloodstream.
Spinal Cord
- The spinal cord is a long, cylindrical structure extending from the foramen magnum to the level of L2.
- The spinal cord contains an H-shaped gray matter surrounded by white matter.
- The gray matter contains neuronal cell bodies and their synapses.
Peripheral Nervous System (PNS)
- The PNS is composed of nerves that extend from the brain and spinal cord to the rest of the body.
- The PNS can be divided into two divisions:
- Somatic nervous system: controls skeletal muscle movement
- Autonomic nervous system: controls smooth muscle, cardiac muscle, and glands.
Cranial Nerves
- The cranial nerves control the sensory and motor functions of the head and neck.
- There are 12 pairs of cranial nerves.
Spinal Nerves
- There are 31 pairs of spinal nerves that control the sensory and motor functions of the body.
- They contain a mixture of sensory and motor fibers.
- Spinal nerves are named according to the level of the spinal cord from which they emerge.
- The spinal nerves branch to form the brachial plexus and the lumbosacral plexus.
Reflexes
- A reflex is a quick, involuntary response to a stimulus.
- Reflexes involve a specific pathway called a reflex arc.
- Reflexes can be: monosynaptic (with one synapse) or polysynaptic (with multiple synapses).
- Examples of monosynaptic reflexes include the knee-jerk reflex and the ankle jerk reflex.
Autonomic Nervous System
- The autonomic nervous system is a branch of the PNS that controls involuntary bodily functions.
- It has two divisions:
- Sympathetic nervous system: responsible for the fight-or-flight response.
- Parasympathetic nervous system: responsible for the rest-and-digest response.
Ganglia
- A ganglion is a collection of neuronal cell bodies located outside of the central nervous system.
- There are three types of ganglia:
- Sensory ganglia: contain the cell bodies of sensory neurons.
- Autonomic ganglia: contain the cell bodies of autonomic neurons.
- Cranial nerve ganglia: are specific to specific cranial nerves.
Definitions
- Sensory (afferent) impulse: carries information towards the CNS
- Motor (efferent) impulse: carries information away from the CNS
- Somatic sensory: refers to sensory information from the body wall structures, and we are acutely aware of this information.
- Autonomic (visceral) sensory: refers to sensory information from blood vessels and internal organs, and we are less aware of this information.
- Voluntary motor: controls skeletal muscle movement
- Autonomic (involuntary) motor: controls smooth muscle, cardiac muscle, and gland function.
### Dermatomes
- A dermatome is a strip of skin supplied by a particular spinal or cranial nerve.
- Dermatomes overlap, thus damage to a single nerve root rarely results in complete loss of sensation in the corresponding dermatome.
Myotomes
- A myotome is a group of muscles innervated by motor nerve fibers from a particular spinal nerve.
Spinal Nerve Injury
- Nerve damage can result from pressure, stretching, or edema.
- Nerve damage can cause dermatomal pain, muscle weakness, or diminished or absent reflexes.
- Herniated intervertebral discs are a common cause of spinal nerve injury.
- Sciatica is a condition in which pain is referred down the leg and foot along the distribution of the sciatic nerve.
Meninges
- The meninges are the three layers of protective membranes that surround the brain and spinal cord.
-
Dura mater– the outermost layer, tough and fibrous with two layers:
- Outer endosteal layer
- Inner meningeal layer
- Arachnoid mater – delicate and spider-like, lies between the dura and pia mater.
- Pia mater – the innermost layer, firmly attached to the brain and spinal cord.
Dural Partitions
- The meningeal dural layer encloses the brain and spinal cord.
- The two layers of dura separate at numerous locations to form dural partitions which project into the cranial cavity and partially subdivide it.
- Falx cerebri
- Falx cerebelli
- Dural sinuses are intracranial venous structures.
Arachnoid Mater
- Delicate and non-vascular connective tissue layer between dura mater and pia mater.
- Ends at the level of S2.
- Separated from dura mater by the subdural space.
- Arachnoid granulations/villi are small finger-like projections of arachnoid mater that project into the dural venous sinuses.
- Allow one-way flow of CSF to the bloodstream.
Spinal Tap
- The spinal tap is usually performed at the L3/L4 or L4/L5 level.
- This is because the spinal cord ends at this level and avoids potential damage.
Peripheral Nervous System
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PNS is divided into somatic and visceral divisions.
- Somatic - controls skeletal muscles (voluntary).
- Visceral - controls smooth and cardiac muscles and glands (involuntary).
- The visceral division can further be divided into sympathetic (fight or flight) and parasympathetic (rest and digest) systems.
Cranial Nerves
- There are twelve pairs of cranial nerves.
- CNI - Olfactory nerve: smell.
- CNII - Optic nerve: vision.
- CNIII, CNIV, CNVI - Oculomotor, Trochlear, Abducent: eye movements.
- CNV - Trigeminal: facial and scalp sensation, mandibular movements.
- CNVII - Facial: facial expression.
- CNVIII - Vestibulocochlear: hearing, balance.
- CNIX, CNX - Glossopharyngeal, Vagus: swallowing, phonation.
- CNXI - Accessory: neck and head movements.
- CNXII - Hypoglossal: tongue movements.
Spinal Nerves
- There are 31 pairs of spinal nerves.
- 8 Cervical nerves (neck and upper limbs).
- 12 Thoracic nerves (upper limbs and thorax).
- 5 Lumbar nerves (abdomen and lower limbs).
- 5 Sacral nerves (lower limbs and perineum).
- 1 Coccygeal nerve.
- They contain a mixture of both sensory and motor fibers.
Spinal Nerve Injury
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Herniated intervertebral disc:
- The posterior part of the anulus fibrosus of the disc ruptures and the centrally located nucleus pulposus is forced out.
- Disc herniations, fractures of vertebral bodies and osteoarthritis of the joints of the vertebra can result in pressure, stretching or oedema of the emerging spinal nerves.
- This can lead to dermatomal pain, muscle weakness and diminished or absent reflexes.
Dermatomes & Myotomes
- It is important to know dermatomes and myotomes for understanding nervous system functions.
- A strip of skin supplied by a particular spinal or cranial nerve is called a dermatome.
- A collection of muscles innervated by motor nerve fibres from a particular spinal nerve is called a myotome.
Reflexes
- The simplest and quickest form of activity in the nervous system.
- Automatic, involuntary response to a stimulus.
- Monosynaptic - a single synapse; examples: knee, ankle.
- Polysynaptic - more than one synapse.
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Stages of a reflex:
- Receptor
- Sensory neuron
- Integration centre
- Motor neuron
- Effector
Ganglia
- Collections of neurons in the PNS.
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Sensory ganglia:
- Found close to the dorsal root of each spinal nerve.
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CN ganglia:
- Found along cranial nerves V, VII, VIII, IX, X.
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Autonomic ganglia:
- Found in paravertebral sympathetic chains around roots of great arteries in the abdomen and in the walls of viscera.
Autonomic Nervous System
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Presynaptic parasympathetic nerve cell bodies are located in:
- Gray matter of the brainstem (CN III, CN VII, CN IX, CN X)
- Gray matter of the sacral segments of the spinal cord (S2-S4)
Important Definitions
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Direction of nerve impulse:
- Sensory (afferent) - toward the CNS.
- Motor (efferent) - away from the CNS.
-
Nature of perception:
- Somatic sensory - acutely aware and well localized (e.g., sharp pain, touch).
- Autonomic (visceral) sensory - barely or vaguely localized, often only perceptible in disease.
-
Type of action:
- Voluntary motor - controls skeletal muscle.
- Autonomic (visceral or involuntary) motor - controls smooth and cardiac muscles and glands.
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Test your understanding of neuroglia and the organization of the nervous system with this quiz. Learn about different types of neuroglia, their functions, and the role of synapses in neuron communication. Perfect for students studying biology or neuroscience.
