Neural control and movement Flashcards
Divisions of the nervous system
Central nervous system (CNS)
1) Brain
Newer more sophisticated regions are piled on top of older, more primitive regions
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
2) spinal cord
- long cylinder of nerve tissue which extends down from the brain stem to the second lumbar vertebrae. 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.
Peripheral Nervous System (PNS)
consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves
1) afferent division
2) efferent division (somatic nervous system AND autonomic nervous system)
- sympathetic division
- parasympathetic division
Afferent division
nerve fibres responsible for bringing sensory information back to the CNS
Efferent division
Somatic nervous system
- nerve fibres that innervate skeletal muscle
Autonomic nervous system
- nerve fibres that innervate smooth muscle, cardiac muscle and glands
–> sympathetic (fight or flight) and parasympathetic (rest and digest)
Neurologia
- comprised about 90% of cells in CNS
- occupy 1/2 of the volume of the brain
Glial cells
there are 4 major types of glial cells that serve as connective tissue of the CNS which help support the neurons physically and metabolically
Neuron
A nerve cell specialized to transmit electrical signals/ pass messages from one part of the body to another.
Consists of:
- cell body
- axon
- dendrites
Cell body
soma, contains nucleus
Axon
a long fiber that conducts impulses away from the cell body
can be known as “nerve fiber”
Dendrites
Short projections from the cell body that transmits impulses toward the cell
Myelin sheeth
discontinuous sheath around the axon, primarily composed of lipids and proteins
- myelinated nerve fibres have a much faster conduction velocity than unmyelinated fibers
Nodes of ranvier
the spaces in between the segments of myelin sheath
synapse
the connection of an axon of one nerve to the cell body or dendrites of another nerve
Multiple sclerosis
Autoimmune disease where the body attacks myelin sheath
- break down in communication
- exposed nerves can be destroyed irreversibly
- fatigue
Neurons can be divided into 3 functional classes
- Afferent neurons: carry impulses from sensory receptors into spinal cord and brain
- Efferent neurons: transmit impulses from CNS out to the effector organs - muscle (motor neurons, glands )
- Inter neurons. Lie entirely in the CNS, they account for 99% of nerve cells
Spinal nerve
- actually a nerve trunk
- it contains hundreds of afferent and efferent nerve fibers that are bound together w/ connective tissue sheaths
Resting membrane potential
Due to selective permeability characteristics of nerve cell fiber, a high potential difference exist inside and outside of nerve fiber. A high concentration of sodium ions outside of the nerve membrane causes it to be electrically positive and on the inside of the nerve membrane electrically negative
Action potential
An appropriate stimuli suddenly causes sodium ions to rush inside of the nerve —> reversal polarity
Once AP has started it spread along the entire length of the nerve fibre
Tetrodotoxin
- blocks sodium channels
- prevent AP in nerve cells
- acts on CNS AND PNS
- death wishing 4-6 hours
Nerve to nerve synapses
- nervous informations relays across synaptic cleft by means of a chemical substance transmitter
- transmitter substances can be other inhibitory or excitatory
What are the impacts of different transmitter substances
They are additive
1. Spatial - when multiple different inputs from different regions add together
2. Temporal- when the same input happens overtime fast enough to add up enough to cause an action potential
Neuromuscular junction
Nerve to muscle synapse
The chemical transmitter substance: acetylcholine
The spinal cord is enlarged in two regions for innervation of the limbs
- Cervical enlargement which extends from C4 through T1 segments of the spinal cord
- Lumbosacral enlargement which extends from T11 through L1 segments of the spinal cord
Structure of spinal nerves
8-Cervical
12-thoracic
5-lumbar
5-sacral
1-coccygeal
Plexus
A network of diverging and converging nerve fibers and blood vessels
Brain and spinal cord are composed of…
White and grey matter
Grey matter
The nerve cell body lie and constitute the grey matter
White matter
Interconnecting tracts of nerve fibers form white matter
What kind of fibres do the following have
a) dorsal roots
b) ventral roots
a) afferent (sensory) fibres that carry information from the periphery to the brain and spinal cord
b) efferent (motor) fibers to the skeletal muscle
Where are the cell bodies of the motor axon making up the ventral roots located?
located in the ventral gray horns of the spinal cord
Where are the cell bodies of the sensory axons making up the dorsal roots located
located outside of the spina cord in the spinal ganglia
Ganglion
a collection of nerve cell bodies located outside the CNS
Spinal cord injury
most often due to trauma to the spinal cord, but can be associated with congenital and degenerative disease.
Transection
transection is complete cut of the spinal cord that results in loss of sensation and voluntary movement inferior to the point of damage
If the cord is transected superior to C5
patient is quadriplegic
What transection will cause the patient may cause the patient to die or have respiratory failure
if the transection is above C4
A patient is paraplegic is the transection occurs where
if the transection occurs below the cervical segment of the spinal cord
ischemia
a deficiency of blood supply to the spinal cord cause by fractures, dislocations, atherosclerosis
–> can lead to muscle weakness and paralysis
proprioceptors
conduct sensory information to the CNS from muscles, tendons, ligaments and joints
kinesthetic sense
gives information about the location of parts of our body in relation to their environment
Muscle spindles
several modified muscle fibres, 4-10 millimeters in length, contained in a capsule with a sensory nerve spiralling down its center.
Spindle fibers
lie parallel to the regular muscle fibers
Function of muscle fibres
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 degree of stretch of the muscle spindles, frequency of impulse transmission up the afferent neuron to the spinal cord progressively increases
3 ways that the muscle spindles can activate the alpha motor neurone to cause the muscle to contract
- Tonic stretch - concerned with the final length of the muscle
- phasic stretch - spindle responds to the velocity of the change of length
- Gamma system - gamma efferent fibers innervate the contractile ends of intrafusal fibers (when alpha motor neurone are activated so are gamma motor neuron)
Stretch reflex
patellar tendon tap
Golgi tendon organ (GTO)
Location: encapsulated in the tendon fibers near the junction of the muscle and the tendon fibers
- approx 1 millimetre long and 0.1 millimetre in diameter
- in series with muscle fibers rather than parallel as are the spindle fibers
- when muscle contracts GTO is stretched
The function of GTO
The firing rate of GTO is very sensitive to changes in tension of the muscle
- sensory input about the tension produced by the muscle is used in a variety of different motor acts such as maintaining a stable grip on an object
- when stimulated by excessive tension or stretch–> sensory information is sent to the CNS–>causes the contracted muscle to relax
Joint receptors
supply information to the CNS regarding joint angle, acceleration of the joint, pain, and pressure
Control of motor functions
the cerebral cortex and cerebellum are the main center employed in learning new motor skills. These areas of the brain initiate voluntary control of movement patterns
