Untitled Quiz

Nervous System Objectives

• Identify and name the brain lobes, major sulci, and gyri
• Describe the concept of functional localization of the brain
• Explain the function of basal nuclei and diencephalon
• Differentiate between types of cerebral white matter
• Identify the parts and describe functions of the brain stem
• State functions of the cerebellum
• Describe the internal and external structure of spinal cords
• Understand the structure of spinal nerves
• Describe major nerve plexuses and their main branches
• Differentiate between sympathetic and parasympathetic divisions of the nervous system

General Organization of the CNS

• The CNS is comprised of the cerebrum, diencephalon, cerebellum, and brainstem
• The cerebrum is the largest part of the brain, controlling higher mental functions
• The cerebrum is divided into hemispheres by the longitudinal fissure
• Each hemisphere consists of grey matter (cell bodies of neurons) forming the cerebral cortex and buried deeply to form diencephalon and basal nuclei
• White matter comprises axons of neurons forming tracts
• The diencephalon is located under the cerebrum and consists of the thalamus, hypothalamus, and epithalamus
• The cerebellum is the second largest part of the brain, composed of two hemispheres covered with cerebellar cortex and inner white matter
• The cerebellum coordinates repetitive smooth body movements and is responsible for body balance and posture
• The brainstem includes the midbrain, pons, and medulla oblongata, which processes information between the spinal cord and cerebrum/cerebellum

Cerebral Cortex

• The folded surface of the cerebral cortex increases surface area
• The elevated folds are called gyri
• The shallow depressions are called sulci
• Deep grooves are called fissures

Grooves and Lobes of the Cerebrum

• The frontal lobe lies in front of the central sulcus
• The parietal lobe lies behind the central sulcus
• The temporal lobe lies below the lateral fissure
• The occipital lobe lies at the back of the brain

Functional Areas of the Cerebrum

• The primary motor cortex is responsible for voluntary movement
• The premotor area is associated with working memory and judgment
• The posterior association area is for speech and language comprehension
• The visual area is for vision
• The auditory area is for hearing
• Broca's area is for motor speech
• The olfactory area is for smell
• The primary somatosensory area is for interpretation of somatosensation (touch)

Deep Grey Matter: Basal Nuclei

• Assist in the regulation of voluntary motor activities
• Modifies instructions sent to skeletal muscles
• Lesions can result in Parkinson's disease

Deep Grey Matter: Diencephalon

• Located under the cerebrum
• Links cerebrum with the brain stem
• Includes thalamus, hypothalamus, and epithalamus

Cerebral White Matter

• Commissural fibers connect areas within the same hemisphere via tracts such as corpus callosum
• Projection fiber tracts connect the cerebrum to lower CNS centers
• Association fibers connect areas within the same hemisphere

Brainstem

• Include the midbrain, pons, and medulla oblongata
• Provide a pathway for ascending and descending tracts
• Contains gray matter nuclei associated with cranial nerves and autonomic centers
• Contains diffuse gray matter (reticular formation) vital for consciousness

Cerebellum

• The second largest part of the brain
• Composed of two hemispheres covered with cerebellar cortex and inner white matter
• Coordinates repetitive smooth body movements
• Responsible for body balance and posture

Protections of the Brain

• Bone: Skull
• Membranes: Dura, arachnoid, and pia mater
• Fluid: Cerebrospinal fluid

Blood Supply to the Brain

• Internal carotid system supplies the cerebrum and diencephalon
• Vertebrobasilar system supplies brainstem, cerebellum, and spinal cord
• Anastomosis between the two systems ensures adequate blood supply

Spinal Cord: Overview

• Spinal cord is shorter than the vertebral column
• CSF in the expanded subarachnoid space between L2 and S2 is called the lumbar cistern
• Dura and arachnoid form the dural sac extending to vertebral level S2

External Features of the Spinal Cord

• Spinal cord ends as conus medullaris at vertebral level L2
• More caudal nerves descend to exit between appropriate vertebrae to form the cauda equina
• Pial extension from conus medullaris forms the filum terminale interna

Spinal Nerves

• 31 pairs of spinal nerves emerge from 31 spinal cord segments (Cervical - 8, Thoracic - 12, Lumbar - 5, Sacral - 5, Coccygeal - 1)

Internal Features of the Spinal Cord

• White matter surrounds the central canal
• Gray matter consists of dorsal horns, lateral horns, and ventral horns

CNS Major Tracts in the CNS

• Sensory information to cerebral cortex
• Integration (processing) and interpretation of sensory input
• Interneuron response to motor neurons for response

Structure of a Nerve

• A nerve is a bundle of neuron fibers
• Each fiber is surrounded by endoneurium
• A bundle of fibers is known as a fascicle surrounded by perineurium
• Fascicles are bound together by epineurium

Cranial Nerves

• Olfactory (I), Optic (II), Oculomotor (III), Trochlear (IV), Trigeminal (V), Abducens (VI), Facial (VII) Auditory (VIII), Glossopharyngeal (IX), Vagus (X), Accessory (XI), Hypoglossal (XII)

Distribution of Cranial Nerves

• Sensory, motor functions, and tests for the specific nerves

Dermatomes and Myotomes

• Dermatome: area of skin innervated by a given spinal level
• Myotome: group of muscles supplied by a given spinal level
• Spinal nerve lesions lead to loss of sensory and motor functions

Nerve Plexuses

• Dorsal and ventral rami are mixed nerves
• Ventral rami blend to create compound nerves
• Each nerve carries axons from 2 or more spinal segments
• The network of ventral rami is called a nerve plexus

Formation of Nerve Plexuses

• Cervical Plexus (C1-C4)
• Brachial Plexus (C5-T1)
• Lumbar Plexus (L1-L4)
• Sacral Plexus (L4-S4)

Major Nerves of the Upper Limb

• Axillary nerve
• Radial nerve
• Musculocutaneous nerve
• Ulnar nerve
• Median nerve

Major Nerves of the Lower Limb

• Femoral nerve
• Lateral femoral cutaneous nerve
• Obturator nerve
• Anterior femoral cutaneous nerve
• Saphenous nerve
• Sciatic nerve
  • Posterior femoral cutaneous nerve
  • Common fibular nerve (superficial and deep branches)
  • Tibial nerve
  • Sural nerve

Overview of the Autonomic Nervous System

• Functions independently without conscious effort
• Regulates the activity of involuntary muscles, cardiac muscles, and glands
• Responds to emotional stress and prepares the body for strenuous physical activity
• Part of the peripheral nervous system

Divisions of Peripheral Nervous System

• Central Nervous System (processes information, stores info, sends orders)
• Peripheral Nervous System (transmits to and from CNS)
  • Somatic (controls skeletal muscles)
  • Autonomic (regulates glands, blood vessels, internal organs)
    • Sympathetic (mobilizes body for action)
    • Parasympathetic (conserves energy)

Somatic Nervous System vs. Autonomic Nervous System

• ANS has two neurons between CNS and effector organs
  • Preganglionic neuron
  • Postganglionic neuron

Overview of Preganglionic and Postganglionic Neurons

• Preganglionic neurons arise from cell bodies in the brain and spinal cord
• Postganglionic neurons emerge from cell bodies in ganglia

Divisions of Autonomic Nervous System

• Neurotransmitters released by postganglionic neurons:
  • Sympathetic: Epinephrine (adrenaline), norepinephrine
  • Parasympathetic: Acetylcholine

Structure of the Autonomic Nervous System

• Both serve the same organs
• Cause opposite effects
• Activities are counterbalanced

Parasympathetic vs Sympathetic Nervous System

• Parasympathetic division brings up relaxed state, allows conservation of energy
• Sympathetic division coordinates the body for the "fight or flight" response

Anatomy of Parasympathetic Division I & II

• Preganglionic neurons located in:
  • Brain nuclei of cranial nerves III, VII, IX, and X
  • Spinal cord segments S2 to S4 (also known as craniosacral division)
• Preganglionic neurons in cranial region travel with cranial nerve fibers, serve head and neck
• Preganglionic neurons in sacral region leave the spinal cord and form pelvic splanchnic nerves
• Postganglionic neurons located in the wall of viscera

Function of Parasympathetic Division

• Decreases heart rate
• Decreases contractility
• Stimulates digestion
• Constrict pupils
• Stimulates salivation
• Bronchial constriction
• Stimulate gallbladder
• Contracts bladder
• Relaxes rectum
• Vaginal lubrication
• Erection

Anatomy of Sympathetic Division

• Preganglionic neurons located in the gray matter of spinal cord segments T1 to L2
• Sympathetic division also known as thoracolumbar division
• Preganglionic neurons exit the spinal cord and enter sympathetic trunk ganglia
• Postganglionic neurons reenter the spinal nerve

Preganglionic Neuron of Sympathetic Division

• Preganglionic neurons located in the spinal cord gray matter
• Exit through ventral root of spinal nerve
• Travel through spinal nerve
• Enter sympathetic trunk ganglia

Postganglionic Neuron of Sympathetic Division

• Postganglionic neurons renter spinal nerve, exit through ventral ramus to effector

Sympathetic Pathways

• Sympathetic trunk ganglion
• Splanchnic nerve
• Collateral ganglion (e.g. celiac)

Function of Sympathetic Division

• Dilates pupils
• Inhibits salivation
• Increases heart rate
• Increases contractility
• Bronchial dilation
• Inhibits digestion
• Stimulates glucose release
• Stimulates epinephrine and norepinephrine release
• Relaxes bladder
• Contracts rectum
• Orgasm
• Ejaculation
• Peripheral vasoconstriction