Neuroanatomy & Neurophysiology Review

Spinal Cord

• The CNS consists of the brain and spinal cord.

• Spinal cord protection is provided by vertebrae, within the vertebral canal.

• Spinal cord protection is also provided by meninges comprised of dura mater, arachnoid mater, and pia mater.

• The spinal cord consists of 31 pairs of spinal nerves.

• The spinal nerves are part of the PNS

• At each vertebra, two spinal nerves emerge on each side (left and right).

• Each spinal nerve carries sensory afferent and motor efferent axons.

• Spinal nerves contain dorsal and ventral roots, connecting the spinal cord to sensory receptors and effectors (muscles & glands).

• The spinal cord includes four regions: cervical, thoracic, lumbar, and sacral.

Spinal Cord Organization

• The tissues of the CNS are divided into gray and white matter.

• Gray matter consists of unmyelinated axons, neuron cell bodies and dendrites, neuroglia, and the central canal filled with cerebral spinal fluid.

• Nuclei are clusters of neuron cell bodies in the CNS, similarly, Ganglion is a cluster of neuron cell bodies in periphery (PNS).

• White matter consists of myelinated axons.

• Tracts are groups of axons bundled together sending AP's to other neuron groups, running from one area in the brain or spinal cord to another, with few cell bodies.

• The corpus callosum includes axons crossing between the hemispheres of the cerebrum.

• Function of the spinal cord is mostly to conduct either sensory or motor information to another part of the nervous system.

• Gray matter is subdivided into horns: dorsal, lateral, and ventral.

• The dorsal gray horn includes sensory neuron axons, as well axons and cell bodies of interneurons.

• The lateral gray horn contains cell bodies of autonomic motor neurons.

• The ventral gray horn contains cell bodies of somatic motor neurons.

• White matter is divided into columns containing tracts consisting of bundles of axons: dorsal, ventral and lateral white columns, sensory tracts, and motor tracts.

Sensory and Motor Tracts

• Doral Columns, Spinothalamic Tract and Dorsal & Ventral Spinocerebellar Tract transfer info

• Doral Columns transfer info about touch, pressure, vibration, and proprioception.

• Spinothalamic Tract transfers info pain, temperature, itch, and tickle.

• Dorsal & Ventral Spinocerebellar Tract transfers proprioception

• Motor Tracts are broken into Direct Motor and Indirect Motor

• Direct Motor (Pyramidal)Pathway causes voluntary movement of skeletal muscle.

• Subcategories of Direct Motor pathways are lateral corticospinal tract, ventral corticospinal tract, corticobulbar tract

• Indirect Motor (Extrapyramidal)Pathway causes involuntary movements regulating posture, balance, and muscle tone

• Subcategories of Indirect Motor pathway include tectospinal tract, vestibulospinal tract, rubrospinal tract, and lateral and medial reticulospinal tract

Reflexes

• A reflex defines a fast, predictable sequence of involuntary actions in response to a particular stimulus.

• Spinal reflexes involve sensory information processed in the spinal cord without input from the brain.

• Sensory information about a stimulus may still be sent to the brain.

The Brain

• Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital.

• The cranium is the protective armor for the brain.

• Meninges (Dura, Arachnoid, Pia mater) surround the brain, acting as a shock absorber.

• The blood-brain barrier is formed by capillary endothelial cells extensively interconnected by tight junctions.

• Only lipid-soluble substances and water can diffuse across the endothelial cell membrane and into the ISF of the brain and spinal cord.

• Passive or active transport mechanisms are required for water-soluble compounds to cross the capillary wall.

• CSF is secreted by the choroid plexus, regions composed of capillaries and ependymal glia cells in the wall of the lateral, third, and fourth ventricles.

• In the CSF pathway, the fluid flows into four interconnected ventricles and through the spinal cord's central canal and into the subarachnoid space.

• CSF is reabsorbed into the circulatory system at venous sinuses.

• Hydrocephalus is a condition where normal CSF drainage is blocked, increasing fluid volume and pressure, which damages the brain.

• A shunt can be used to take excess CSF from the ventricle to the spinal cord's central canal to drain back to the venous sinus and into the circulatory system until eliminated by body as urine

Brain Parts

• The brain consists of the cerebrum, diencephalon (thalamus, hypothalamus, pineal gland), cerebellum, and brain stem (midbrain, pons, medulla oblongata).

Brain Stem

• The brain stem (medulla, pons, midbrain) is the transition from the spinal cord to higher brain centers.

• The Medulla Oblongata is the transition from the spinal cord to the brain proper.

• In the medulla, crossover of tracts between the spinal cord and cerebral cortex forms the Pyramids.

• Nuclei in the medulla control the following involuntary functions: heart rate and blood pressure, respiration, swallowing, vomiting

• The Pons is a bulbous protrusion above the medulla and a relay station from each side of the cerebellum to and from the cerebral cortex.

• Nuclei in the pons influence respiration.

• The midbrain (mesencephalon) is a small area between the lower brainstem and diencephalon.

• The midbrain includes the superior and inferior colliculus.

Cerebellum and Diencephalon

• The cerebellum coordinates movement, executes voluntary movements by modifying skeletal muscle activity, and regulates posture and balance.

• Equilibrium and balance are from inner ear receptors.

• Cerebellar dysfunction results in problems with walking, balance, and accurate hand and arm movement.

• The thalamus relays and integrates sensory input, enabling crude sensations of pain, temperature, and pressure.

• The hypothalamus regulates homeostasis, hunger, thirst, and endocrine function, including pituitary production and secretion of hormones.

• The pineal gland secretes melatonin, controlling circadian rhythms.

• Circadian rhythm: 24-hour light-dark cycle

• The suprachiasmatic nucleus (SCN) of the hypothalamus has intrinsic activity synchronized with sensory information (light cycles) received through the eyes.

• Melatonin (pineal gland) is linked to circadian rhythms disrupted by shift work and jet lag.

• Shifts in light-dark cycles can cause sleep disturbances, depression, seasonal affective disorder, and diabetes/obesity.

Brain's Gray matter

• The Corpus callosum connects the two hemispheres via axons from one side of the cerebral hemisphere to the other.

• Gray matter is divided into three regions: cerebral cortex (outer layer of cerebrum), basal ganglia, and the limbic system.

-The basal ganglia (basal nuclei) control movement, suppress unwanted movement, and regulate muscle tone, whereas the limbic system links higher cognitive functions and emotions.

• The major areas of the limbic system include the amygdala and cingulate gyrus (emotion and memory) and the hippocampus (learning and memory).

• Parkinson's disease results from the destruction of basal nuclei neurons that produce the neurotransmitter dopamine.

• Patients with Parkinson's show increased muscle tone and rigidity, slow to initiate or stop a movement.

• Oral or injectable dopamine is ineffective for Parkinson's because it cannot cross the blood-brain barrier (BBB).

• Treatment for Parkinson's involves giving the dopamine precursor "L-dopa”, which can cross the BBB via an amino acid transporter into ISF, enabling neurons to metabolize it to dopamine, thus restoring dopamine levels.

• The newest treatments involve implantation of fetal stem cells, which establish, grow, and produce dopamine.

Brain Stem and Cranial Nerves

• The brain stem is the oldest region of the brain, consisting of the medulla, pons, and midbrain.

• Eleven of the twelve cranial nerves originate from the brainstem, and Cranial nerves can include sensory, motor, or mixed nerves for the head, neck, and many organs.

• Many nuclei connect through the reticular formation (Reticular Activating System), a web of interconnected neurons from the brainstem up through the brain that controls wakefulness/sleep, muscle tone, pain modulation, stretch reflexes, breathing and blood pressure.

Reticular Activating System (RAS)

• Neurons mainly originate in the reticular formation of the brainstem projecting their axon to large areas of the brain.

• Arousal, or awakening from sleep, involves increased RAS activity, and sensory stimuli activates RAS which activates the cerebral cortex resulting in consiousness.

• The Cerebrum is the largest part of the brain and provides intelligence.

• Functions from a viewpoint divided into Sensory areas, Motor Areas and Associtation areas Sensory input translated into perception (awareness)

• Direct Differences between the cerebral Hemispheres include Hemispheric lateralization (cerebral dominance) involving left-brain and right-brain dominance.

Functional Cortex Areas

• Primary motor cortex
• Premotor cortex
• Prefrontal cortex
• Broca's area
• Orbitofrontal cortex
• Primary auditory cortex
• Auditory association area
• Central Sulcus
• Primary Somatosensory Cortex
• Somatosensory- association area
• Parietal lobe
• Common intergrative area
• Wernicke's area
• Visual association area
• Primary Visual cortex
• Occipital lobe
• Temporal lobe
• Gustatory cortex
• Insula
• Olfactory Cortex

Senses

• Special senses have devoted regions of the brain: Primary visual cortex, Primary auditory cortex, Olfactory cortex , Gustatory cortex

• Primary visual cortex: Occipital lobe - receives information from the eyes (vision).

• Primary auditory cortex: Temporal lobe - receives information from the ears (sound).

• Olfactory cortex: Temporal lobe - receives information from the chemoreceptors in the nose (smell).

• Gustatory cortex: Insula - receives information from the taste buds.

• Neural pathways extend from sensory areas to association areas, integrating stimuli into perception

Sensory Info

• Information enters the spinal cord and acts without input from the brain, but the sensory information about a stimulus can be sent to the brain so that the brain creates a perception of the stimulus.

• Primary somatic sensory cortex (AKA somatosensory cortex, sensory strip, post-central gyrus) is located in the parietal lobe.

• The termination point for pathways from the skin, musculoskeletal system, and viscera; somatosensory pathways carry information about touch, temperature, pain, itch, vibration, and body position (proprioception)

• The right side of the body's sensations receive somatic sensations from the right side of the skin and vice versa; damaging the cortex reduces skin sensitivity opposite the body.

• Primary motor cortex can be called a motor strip, pre-central gyrus, and motor association, The point where pathways from the body terminate, controling skeletal muscles.

Homunculus

• Displays proportion to innervation of muscle group rather than physical space.
• Larger areas relate to muscle groups such as hands, face
• Smaller areas relate to muscle groups such as trunk, feet, thigh

Hemispheric lateralization

• Refers to differnt functions in each hemisphere of the brain and include

-The right hemisphere which recieves controls recieves info from the left side of the body is more active in artistic and creative tasks

• The left hemishere controls info from the right side of the body and is active in logic based tasks

Language

• Language is understood in Wernicke's area and put together by Broca's area.

• Damage to Wernicke's area results in being unable to retrieve words.

• Damage to Broca's area results in word salad and a compromised expression.

• Sleep exists as an easily reversible state of inactivity without external environment interaction.

• Non-rapid eye movement sleep (NREM) includes with stages 2/3, having smaller frequence waves.

• During rapid eye movement sleep (REM), the brain inhibits motor neurons to skeletal muscles, temporarily paralyzing the muscles and leading to dreaming.

• NREM Sleep Stages progresses from stage 1 to stage 4.

• Wakefulness transition: the person is relaxed with closed eyes has fleeting thoughts with both eyes closed and fleeting thoughts.

• During light sleep with 2 is easy to awake, during sleep period 3 is a difficult but not the most, Stage 4: is the deepest level of sleep, and is the deepest level of sleep.

• Person falls asleep by sequentially going through all four stages of NREM sleep and NRÉM in reverse order before entering into REM sleep.

• Intervals of NREM and REM alternate through the night for about 4 -5 times with hours of sleep equal to 8 - insomina consists of the inability to sleep

• Sleep apnea involves during sleep's normal breathing cessation

• Somnambulism means to sleepwalk, most common in children.

Test your knowledge of the brain! Topics covered include the cerebellum, hypothalamus, corpus callosum, suprachiasmatic nucleus, neurotransmitters, limbic system, and spinal cord. This quiz assesses understanding of neuroanatomy and neurophysiology.