Final Flashcards
What is the Brain?
evolutionarily newer more sophisticated regions are piled on top of older, more primitive regions
2 Parts of the Central Nervous System
Brain and Spinal Cord
What are the regions of the brain
a) Forebrain
(i) Cerebrum constitutes about 80% of total brain weight
- cerebral cortex, basal nuclei
(ii) Diencephalon - thalamus, hypothalamus
b) Cerebellum
c) Brainstem - continuous with the spinal cord - medulla, pons, midbrain
What is the Spinal Cord
long cylinder of nerve tissue which extends down from the brainstem to the second lumbar vertebrae.
Explain the spinal cord (dimensions and parts)
45 cm long and 2 cm in diameter. Protected by the vertebral column and associated ligaments and muscles, the spinal meninges and the cerebrospinal fluid.
What does the Peripheral Nervous System consist of?
Consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves
What are the Two divisions
Afferent and Efferent
Explain Afferent Division
conveys information from the sensors in the periphery to the central nervous system (CNS)
What are the Two of the nervous systems in Efferent Division?
Autonomic and Somatic
Somatic?
Somatic nervous system - nerve fibers innervate skeletal muscle
Autonomic?
Autonomic nervous system - nerve fibers innervate smooth muscle and cardiac muscle and glands
The two divisions in Autonomic?
(i) sympathetic division – fight or flight
(ii) parasympathetic division – rest and digest
Explain Neuroglia
comprise about 90% of the cells within the CNS. They occupy about half of the volume of the brain. The four major types of glial cells serve as the connective tissue of the CNS and as such help support the neurons both physically and metabolically.
How many neurons and how many neuroglia?
It is estimated that there are 100 billion neurons in the brain and one trillion neuroglia.
What does the nervous system do?
Along with the endocrine system, the nervous system regulates and coordinates the various functions of the body.
Basic structures of the nerve?
Neuron, Cell Body, Axon and Dendrite
What is a Neuron?
a nerve cell. A neuron is specialized to transmit electrical signals.
What is a Cell body?
Cell body - soma - contains the nucleus
What is the Axon?
Axon - a long fiber that conducts impulses away from the cell body. The term “nerve fiber” is often used in reference to an axon.
What is the Dendrite?
Dendrite - short projections from the cell body that transmit impulses toward the cell body
Main purpose of the neuron?
to pass messages (impulses) from one part of the body to another
What is around the axon?
Myelin Sheath - a discontinuous sheath around the axon. It is primarily composed of lipids and proteins.
Nodes of ___?
Nodes of Ranvier - spaces between the segments of myelin sheath –> saltatory conduction
Difference between Myelinated nerve fibres and unmyelinated fibers?
Myelinated nerve fibers have much faster conduction velocities than unmyelinated fibers
What is the Synapse?
the connection of an axon of one nerve to the cell body or dendrites of another nerve.
Saltatory Conduction?
(hop or leap) Signals leaps from node to node
Explain the steps of Multiple Sclerosis?
- Autoimmune disease - body attacks myeline sheath
- Break down in communcation
- Exposed nerves can be destroyed irreversibly
Fatigue, vision changes, numbness, loss of coordination, muscle weakness, cognitive dysfunction
Neurons can be divided into 3 functional classes:
Afferent neurons, Efferent Neurons and Interneurons
Afferent neurons?
carry impulses from the sensory receptors into spinal cord or brain
Efferent neurons?
transmit impulses from the CNS out to the effector organs - muscles (motor neurons) and glands
Interneurons?
lie entirely within the CNS. They account for 99% of all nerve cells.
Each spinal nerve is actually a nerve ___?
Trunk - it contains hundreds of individual afferent and efferent nerve fibers that are bound together by connective tissue sheaths.
The two potentials in the Nerve Impulse?
Resting membrane potential and Action potential
Explain Resting membrane potential?
due to the selective permeability characteristics of the nerve cell membrane, a potential difference (voltage) exists between the inside and outside of the nerve fiber. A high concentration of positive sodium ions on the outside of the nerve membrane causes it to be electrically positive, while the inside of the nerve is electrically negative.
Action potential
an appropriate stimulus suddenly causes sodium ions to rush to the inside of the nerve –> reversal of polarity. Once the action potential is started, it spreads along the entire length of the nerve fiber
Nerve to Nerve synapses?
Nervous information is relayed across the synaptic cleft by means of a chemical transmitter substance.
Transmitter substances can be either?
excitatory or inhibitory in their effects on the post synaptic membrane potential.
The impacts of different transmitter substances are additive, they ___? Summation can be ___ and ___?
Sum. Summation can be Spatial and can also be Temporal
Spatial Summation
when multiple inputs from different regions add together.
Temporal Summation
when the same input occurs over time fast enough to add up enough to cause an action potential.
Neuromuscular Junction
nerve to muscle synapse. The chemical transmitter substance is acetylcholine.
The spinal cord is?
enlarged in two regions for innervation of the limbs
The two regions?
- The cervical enlargement which extends from the C4 through T1 segments of the spinal cord
- The lumbosacral enlargement which extends from the T11 through L1 segments of the spinal cord
What is the Plexus?
a network of converging and diverging nerve fibers, or blood vessels.
The brain and spinal cord are composed of what?
Gray matter and white matter. The nerve cell bodies lie in and constitute the gray matter while the interconnecting tracts of nerve fibers (axons) form the white matter.
Structure of spinal nerves?
31 pairs of spinal nerves are attached to the spinal cord – 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal
Each spinal nerve has a ____ root and a ____ root connected to what?
Dorsal root and a Ventral root connected to the spinal cord.
The dorsal root contains:
The dorsal roots contain afferent (sensory) fibers that carry information from the periphery to the spinal cord and brain.
The ventral roots contains:
The ventral roots contain efferent (motor) fibers to the skeletal muscle.
JIM CARTER STAR:
The cell bodies of the ____ axons making up the ___ roots are located where?
The cell bodies of the ___ axons making up the ___ roots are located where?
What is a Ganglion?
motor axons making up the ventral roots, in the ventral gray horns of the spinal cord
Sensory axons making up the dorsal roots, outside of the spinal cord in the spinal ganglia.
Ganglion – a collection of nerve cell bodies located outside of the CNS.
Spinal cord injury?
transection of the spinal cord results in loss of all sensation and voluntary movement inferior to the point of damage.
If the patient is quadriplegic:
The cord is transected superior to C5
If the transection is above C4:
The patient may die of respiratory failure
If the patient is paraplegic
paralysis of both lower limbs - if the transection occurs below the cervical segment of the spinal cord.
Fractures, dislocations and atherosclerosis cause:
What does it affect?
Deficiency of blood supply (ischemia) to the spinal cord affects its function and can lead to muscle weakness and paralysis.
If the brain or spinal cord is damaged
In most cases the injured axons do not recover.
One type of Muscle Sense Organs:
Proprioceptors - conduct sensory information to the CNS from muscles, tendons, ligaments, and joints –> kinesthetic sense
Muscle Spindles (Change in Length) Structure:
several modified muscle fibers, four to 10 millimeters in length, contained in a capsule, with a sensory nerve spiraling around its center.
Spindle fibers (intrafusal fibers) lie parallel to the regular fibers (extrafusal fibers).
Muscle Spindles Function:
send information to the CNS regarding the degree of muscle stretch –> activation of the exact number of motor units to overcome a given resistance. With increasing degrees of stretch of the muscle spindle, the frequency of impulse transmission up the afferent neuron to the spinal cord progressively increases.
Three ways that the muscle spindle can activate the alpha motor neurons to cause the muscle to contract:
- Tonic stretch - concerned with the final length of the muscle fibers
- Phasic stretch - spindle responds to the velocity of the rate of length change
- Gamma system - gamma efferent fibers innervate the contractile ends of the intrafusal fibers. When the alpha motor neurons are activated, the gamma motor neurons are also activated (coactivation).
Gamma system provides what?
the mechanism for maintaining the spindle at peak operation at all muscle lengths.
The patellar tendon tap is an example of?
Stretch Reflex
Muscle Spindles:
senses stretch, initiates signal down sensory (afferent) neuron, integrated in spinal cord, stimulating both alpha (extrafusal) and gamma (intrafusal) efferent motor neuron stimulation and muscle contraction.
Distributed throughout the muscle. Their density varies with the degree of control required by a given muscle.
Golgi Tendon Organs (Change in tension) location
encapsulated in tendon fibers near the junction of the muscle and tendon fibers. They are approximately one millimeter long and 0.1 millimeters in diameter. They are in series with the muscle fibers rather than in parallel as are muscle spindles.
When a muscle contracts,
the GTO is stretched. The firing rate of the GTO is very sensitive to changes in the tension of the muscle.
Sensory input from GTO about the tension produced by muscles is useful for…
a variety of motor acts, such as maintaining a steady grip on an object. It regulates muscle tension within an optimal range.
When stimulated by excessive tension or stretch…
–> send sensory information to the CNS –> causes the contracted muscle to relax (reflex inhibition) - protect the muscle and its connective tissue harness from damage due to excessive loads
Joint receptors (Change in angle)
Supply information to the CNS concerning joint angle, acceleration of the joint, etc.
What are the main centres employed in learning new motor skills? And what do they initiate?
The cerebral cortex and cerebellum
These areas of the brain initiate voluntary control of movement patterns.
The cerebrum
is the anterior-most and the largest part of the brain. It is split down the middle into two cerebral hemispheres. The right cerebral hemisphere receives sensations from and controls movements on the left side of the body. The left cerebral hemisphere is concerned with sensations and movements on the right side of the body.
Cerebral Cortex
is the 3 to 4 millimeter thick outer layer of gray matter of the cerebrum, responsible for higher brain functions such as sensation, thought, reasoning, memory, and voluntary muscle movement.
Primary motor cortex
located at the rear of the frontal lobe of the cerebral cortex. Stimulation of different areas of the primary motor cortex brings about movement in different, specific areas of the body. Contains the motor homunculus. However, no coordinated movement can be elicited.
The motor cortex on each side of the brain primarily controls muscles on the ___ side of the body.
Opposite
Corticospinal tract
Corticospinal tract - long axons which carry impulses from the primary motor cortex where their cell bodies are located directly to lower motor neurons in spinal cord —> spinal nerves. The primary motor neurons cross over in the pyramids of the medulla.
The corticospinal system primarily …
mediates performance of fine, discrete, voluntary movements of the hands and fingers.
Premotor cortex
Premotor cortex - one of the three higher areas that command the primary motor cortex. Located on the lateral surface of each cerebral hemisphere in front of the primary motor cortex.
Extrapyramidal tract
Extrapyramidal tract – multi-neuronal pathways - route used to send impulses from the premotor area down to the lower motor neurons of the spinal cord.
Instead of synapsing directly with motor neurons, this pathway involves many of the other brain regions, including the cerebellum.
These pathways are more concerned with posture and coordination of large muscle groups.
Considerable complex interaction and overlapping of function exist between these two systems.
Cerebellum
Located behind the brainstem and under the occipital lobes of the cerebral hemispheres. It functions by means of intricate feedback circuits to monitor and coordinate other areas of the brain involved in motor control.
What does the cerebellum receive?
It receives signals concerning motor output from the cerebral cortex and sensory information from receptors in muscles, tendons, joints and skin, as well as from visual, auditory and vestibular end organs.
Cerebellum function:
Function - the major comparing, evaluating, and integrating center for postural adjustments, locomotion, maintenance of equilibrium, perceptions of speed of body movement, and general motor coordination.
Damage to the cerebellum results
in impaired motor control.
Individuals with severe cerebellar damage cannot start or stop movements quickly or easily. They cannot easily combine the movements of several joints into a single, smooth, coordinated motion.
