STRUCTURAL AND FUNCTIONAL ORGANIZATION OF THE CENTRAL NERVOUS SYSTEM Flashcards
Spinal Cord Structure
(1) The spinal cord is located within the vertebral canal.
(2) Protected by the vertebral column, vertebral ligaments, meninges and cerebrospinal fluid
(3) Meninges are three layers of connective tissue
(a) Dura mater: outer most layer; tough dense connective tissue
(b) Arachnoid mater: middle layer; extends into subarachnoid space, resembles spider web
(c) Pia mater: inner layer, thin and delicate, adheres to surface of spinal cord and brain, contains blood vessels
(4) Subarachnoid space is between the arachnoid and pia mater and is filled with cerebrospinal fluid
(5) Epidural space has fat which helps protect/cushion
(a) Between vertebrae and dura mater
Gross Anatomy of the Spinal Cord
(1) Extends from the medulla oblongata to the second lumbar vertebra
(2) Two grooves divide the spinal cord into two hemispheres
(a) Anterior median fissure
(b) Posterior median sulcus
(3) White matter surrounds a H shape gray matter
(4) Central canal is filled with cerebrospinal fluid and is located in the center of the gray matter.
(5) Spinal nerves are a path of communication between the spinal cord and specific regions of the body.
(6) The spinal cord has 31 pairs of spinal nerves
(7) Roots: Are two bundles of axons that connect each spinal nerve to a segment of the cord.
(a) Posterior (dorsal) root contains sensory axons which conduct nerve impulses from sensory receptors (afferent)
(b) Anterior (ventral) root contains axons of motor neurons (autonomic and somatic) which conduct nerve impulses from the CNS to the effectors (efferent)
The spinal cord white and gray matter have two major functions
(a) White matter has tracts that serve as highways for nerve impulses.
(b) Gray matter of the spinal cord receives and integrates incoming and outgoing information and is a site for integration of reflexes.
Gray matter:
(a) Contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia
(b) Gray matter is subdivided into left and right regions called horns named relative to their locations (anterior, lateral and posterior)
1) Posterior horn contains cell bodies and axons of interneurons as well as axons of incoming sensory neurons.
2) Anterior (ventral) gray horns contain cell bodies of somatic motor neurons that provide impulses for contraction of muscles
3) Lateral gray horn is present only in the thoracic and upper lumbar segments and contain cell bodies of autonomic motor neurons that regulate the cardiac muscle, smooth muscles, and glands.
White Matter:
Consists of myelinated axons and is organized into columns
(a) Each column contains one or more tracts which are bundles of axons
(b) Sensory tract (ascending) tract: consist of axons that conduct nerves impulses toward the brain
1) Example: Spinothalamic tract
(c) Motor (descending) tracts: Consists of axons that conduct nerves impulses away from the brain
1) Example: Corticospinal tract
Reflexes
Fast, involuntary sequences of actions in response to stimuli
(a) Can be simple (withdrawal) or complex (learned sequence such as driving car)
(b) Levels
1) Spinal reflex: Simple (reflex arc) Example: Patellar reflex
2) Cranial reflex: Simple; occurs in the brainstem.
Example: Gag reflex
Identify the composition and distribution of the spinal nerves
Spinal Nerves
(1) Spinal nerves are part of the peripheral nervous system.
(2) They connect the CNS to the sensory receptors and muscles of the body.
(3) 31 pairs of spinal nerves named according to the level of the vertebral column from which they emerge.
(a) 8 pairs of cervical
(b) 12 pairs of thoracic
(c) 5 pairs of lumbar
(d) 5 pairs of sacral
(e) 1 pair of coccyx
(4) Each spinal nerve is connected to the spinal cord by the anterior (motor) and posterior (sensory) root.
(a) Sensory information goes through dorsal root
(b) Motor information goes through anterior root.
(5) Each spinal nerve contains layers of protective connective tissue coverings
(a) Individual axons wrapped in endoneurium
(b) Groups of axons arranged in bundles called fascicles
(c) Fascicles wrapped in perineurium
(d) Epineurium is the superficial covering over entire nerve
Identify the composition and distribution of the spinal nerves
Distribution of Spinal Nerves
(1) Many spinal nerve branches join axons from adjacent nerves to form networks called plexuses.
(a) Cervical plexus supplies posterior head, neck, upper part of the shoulder and the diaphragm
1) Example: Phrenic nerve (C3, C4, C5) innervates the diaphragm to contract
(b) Brachial plexus: upper limbs, some neck and shoulder muscles
1) Examples: Radial nerve (C5-T1), Ulnar nerve (C8-T1), Axillary nerve (C5- C6)
(c) Lumbar plexus: Abdominal wall, external genitals and parts of the lower limbs
1) Example: Femoral nerve (L2-L4)
(d) Sacral plexus: Buttocks, perineum and most of lower limbs
1) Example: Sciatic nerve (L4-S3)
2) Some spinal nerves branches extend directly to body structures
a) Spinal nerves T2-T11 are called intercostal nerves
(1 Supply muscles of abdomen and between the ribs, skin of chest and back
Identify how the brain is protected and supplied with blood.
Brain Protection
(1) Cranium (skull)
(2) Cranial Meninges
(a) Dura mater: Outer most layer
(b) Arachnoid mater: Middle layer
(c) Pia mater: Inner layer
Identify how the brain is protected and supplied with blood.
Brain Blood Supply and the Blood Brain Barrier
(1) Only 2% of the body’s weight, but requires 20% of the body’s oxygen supply.
(a) Brain neurons totally deprived of oxygen for four or more minutes may lead to permanent damage
(b) Brain requires continuous glucose supply, which it receives via blood
(c) “Circle of Willis” is a circulatory anastomosis that supplies blood to brain and surrounding structures; stems from the two internal carotid arteries.
(2) Blood brain barrier protects the brain cells from harmful substances and pathogens.
(a) Allows passage of lipid soluble materials such as O2, CO2, alcohol, anesthesia
(b) Consists of tightly sealed blood capillaries and astrocytes.
(c) Can be broken down by trauma, certain toxins, and inflammation.
Identify how the brain is protected and supplied with blood.
Cerebrospinal Fluid
(1) Clear, colorless liquid that cushions the brain, carries oxygen, glucose and other needed
chemicals from the blood to neurons and removes waste.
(2) Circulates through the subarachnoid space around the brain and spinal cord, central canal, and through cavities in the brain called ventricles.
(3) Produced in the choroid plexuses located in the brain
(4) Slowly reabsorbed into the blood through the arachnoid villi
Name and Explain the function of the major parts of the brain.
Major Parts:
(1) Brain Stem
(a) Continuous with spinal cord; contains the medulla oblongata, pons, and midbrain
(2) Diencephalon
(a) Superior to brain stem; contains thalamus, hypothalamus, and pineal gland
(3) Cerebellum
(a) Means “little brain;” lies posterior and inferior
(b) Functions for balance and equilibrium and coordination
(4) Cerebrum
(a) Largest, most superior part
Name and Explain the function of the major parts of the brain.
Brain Stem
(1) Three major regions
(a) Medulla Oblongata
1) Forms the inferior part of the brain stem; a continuation of spinal cord .
2) Its white matter contains all sensory and motor tracts between spinal cord and brain
3) Gray matter contains nuclei where neurons form synapses with one another
a) Cardiovascular center regulates the rate and force of the heart and the diameter of the vessels
b) Medullary rhythmicity area regulates breathing
4) Nuclei associated with touch, pressure, vibration and proprioception lie in the posterior part of the medulla.
5) Contains nuclei associated with cranial nerves VIII-XII
(b) Pons
1) “Bridge” which connects the medulla to the midbrain and above
2) Contains ascending (sensory) and descending (motor) tracts
3) Connects left and right sides of the brain
4) Contains nuclei
a) Motor relay from cerebrum to cerebellum
b) Helps control breathing
c) Contains nuclei associated with cranial nerves V
(c) Midbrain
1) Connects the pons to the diencephalon
2) Cerebral peduncles: Large tracts that contain axons of motor neurons from cerebrum to rest of brainstem and spinal cord
3) Substantia nigra: Loss of these neurons related to Parkinson disease
4) Red nuclei: Coordinate muscular movement
5) Contains nuclei associated with cranial nerves CN III and IV
6) Superior colliculi involved in scanning eye movement and responses to visual stimuli
7) Inferior colliculi response to auditory input and startle reflex
Name and Explain the function of the major parts of the brain.
Diencephalon
(1) Three major regions
(a) Thalamus
1) Major sensory relay center
2) Contributes to motor functions
3) Plays role in consciousness
(b) Hypothalamus
1) Lies inferior to thalamus and superior to the pituitary gland; important for homeostasis
2) Control of pituitary and hormone production
3) Control and integration of the ANS
4) Regulation of emotional and behavior patterns
5) Regulation of eating and drinking
6) Control of body temperature
7) Regulation of circadian rhythms, sleep and awakening patterns
(c) Pineal Gland (part of the endocrine system)
1) Secretes melatonin which promotes sleepiness and contributes to setting the body’s biological clock
Name and Explain the function of the major parts of the brain.
Cerebellum
(1) Location: Posterior to medulla and pons, inferior to cerebrum and attached to brain stem by cerebellar peduncles
(2) Structure:
(a) Two cerebellar hemispheres
(b) Cerebellar cortex: Gray matter
(c) Tree-like appearance (seen in sagittal section) of white matter and gray nuclei
(3) Functions
(a) Receives wide range of sensory input from muscles, joints, tendons, eyes, equilibrium receptors in inner ears and visual receptors
(b) Compares actual movements with intended ones
(c) Helps to smooth and coordinate skeletal muscle contractions
(d) Helps execute skilled motor activities
(e) Regulates posture and balance essential for skilled motor activities
