CNS Flashcards
Functions CNS
control of internal environment
voluntary control of movement
spinal cord reflexes
CNS consists of
brain
spinal cord
PNS
neurons outside the CNS
Sensory division
detects stimuli and transmits information from receptors to CNS
somatic sensory
visceral sensory
Motor divison
initiates and transmitts info from CNS to effectors
somatic motor
autonomic motor
Somatic sensory
sensory input that is consciously perceived from receptors
e.g., eyes, ears and skin
Visceral sensory
sensory input that is not consciously perceived from the receptors of blood vessels and internal organs
Somatic motor
motor output that is consciously or voluntarily controlled
effector is skeletal muscle
Autonomic motor
motor output that is not consciously or is involunatry controlled
effectors are cardiac muscle, smooth muscle and glands
Axon
carries electrical message (action potential) away from cell body
covered by Schwann cells
Schwann cells
forms myelin sheath
Synapse
contact points between axon of one neuron and dendrite of another neuron
Greater speed of neural tranmission
increase diameter of axon
increase myelin sheath
Resting membrane potential
negative charge inside cells at rest (polarized)
-5 to -100mv
-40 to -75mv in neurons
Magnitude of resting membrane potential determined by:
- permeability of plasma membrane to ions
- difference in ion conc across membrane
What regulates ion passage across cell membrane?
channels
Exchange of sodium and potassium across cell membrane
maintained by sodium-potassium pump
2K+ in
3Na+ out
Action potential
occurs when a stimulus of sufficient strength depolarizes the cell
open Na+ channel and Na+ diffuses out
=inside becomes more positive
Repolarization
return to resting membrane potential
K+ leaves the cell rapidly
Na+ channels close
All or none law
once a nerve impulse is initiated it will travel the length of the neuron
Neurotransmitter
chemical messenger released from presynaptic membrane
binds to receptor on postsynaptic membrane
causes depolarization of postsynaptic membrane
Excitatory postsynaptic potentials
promote neural depolarization
temporal summation
spatial summation
Temporal summation
rapid, repetitive excitation from a single excitatory presynaptic neuron
Spatial summation
summing EPSPs from several different presynaptic neurons
Inhibitory postsynaptic potentials
causes hyperpolarization (more negative resting membrane potential)
neurons with more negative membrane potential resist depolarization
EPSP > IPSP
neuron moves towards threshold
Joint proprioceptors
- free nerve endings (touch, pressure)
- golgi type receptors (found in joint ligaments)
- pacinian corpuacles (tissues around joints/skin)
Muscle proprioceptors
muscle spindles
golgi tendon organs
Proprioceptors
sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give info about the position of the limb in space
Muscle spindles
respond to changes in muscle length
Muscle spindles consist of
Intrafusal fibres - run parallel to normal muscle fibres
Gamma motor neurons - stimulate intrafusal fibres to contract with extrafusal fibres (by alpha motor neuron)
Stretch reflex
stretch on muscle causes reflex contraction
knee-jerk reflex
Muscle spindle structure
- detect stretch of muscle
- sensory neurons conduct action potentials to spinal cord
- sensory neurons synapse with alpha motor neurons
- stimulation of the alpha motor neuron causes the muscle to contract and resist being stretched
Muscle spindles function
assist in the regulation of movement M
maintain posture
Golgi tendon organs
monitors force development in muscle
prevent damage during excessive force generation
stimulation results in reflex relaxation of muscle
Ability to voluntarily oppose GTO inhibition related to
gains in strength with training due to increased tendon stiffness
Golgi tendon organ structure
- golgi tendon organs detect tension applied to a tendon
- sensory neurons conduct action potentials to the spinal cord
- sensory neurons synapse with inhibitory interneurons that synapse with alpha motor neurons
- inhibition of the alpha motor neuron causes muscle relaxation, relieving the tension applied to the tendon
Muscle chemoreceptors
sensitive to change in chemical environment surrounding a muscle - H+, CO2 and K+
inform CNS about metabolic rate of muscular activity - regulate cadiovascular/pulmonary responses
Structure motor unit
motor neurons located within spinal cord
responsible for carrying neural messages from spinal cord to skeletal muscles
Motor unit
motor neuron and all the muscels fibres it inneravtes
Innervation ratio
low ratio in muscle involved in fine motor control
high ratio in muscle not require fine motor control
Motor unit recruitment
recruitment of additional muscle fibres by activating more motor units
Size principle
smallest motor units recruited first during exercise
sequential recruitment of motor units during exercise
Type I
slow-twtich
smallest
Type IIa
intermediate
fast-twitch
fatigue resistant
Type IIx
largest
fast-twitch
fatiguable
Recruitment pattern during incremental exercise
Type I –> Type IIa –> Type IIx
Cerebrum/cerebral cortex function
- organization of complex movement
- storage of learned expereince
- reception of sensory information
Cerebellum
implicated in control of movement and integration of sensory information
Brainstem
role in cardiorespiratory function, locomotion, muscle tone, posture, receieving info from special senses
Midbrain
mesencephalon
connects the pons and cerebral hemispheres
Functions midbrain
control responses to sight
eye movement
pupil dilation
body movement
hearing
Medulla oblongata
involved in control of autonomic function
relaying signals between the brain and spinal cord
coordination of body movements
Pons
involved in sleep and the control of autonomic function
relays sensory info between the cerebrum and cerebellum
Spinal cord
45cm long
encased and protected by bony vertebral column
attaches to brainstem
major conduit for 2-way transmission of info from skin, joints and muscle to brain
Spinal cord neurons
motor neuron
sensory neuron
interneuron
Spinal tuning
intrinsic neural networks within spinal cord that refine voluntary movement after receiving messages from higher brain centres
Withdrawal reflex
occurs via a reflex arc
reflex contraction of skeletal muscles can occur in response to sensory input and is not dependent on the activation of higher brain centres
Control of voluntary movement
involves cooperation of many areas of brain along with subcortical areas
motor cortex receives inputs from variety of brain areas including basal nuclei, cerebellum, thalamus
spinal mechanisms - refinement of motor control
feedback from proprioceptors allows for further modofication in motor control
Withdrawal reflex process
- sensory neurons from pain receptors conduct action potentials to the spinal cord
- sensory neuron synapse with excitatory interneurons
- excitatory interneurons stimulate alpha motor neurons that innervate flexor muscles = withdrwal
- collateral branches of sensory neurons synapse excitatory interneurons that cross opposite side of spinal cord
- excitatory interneurons that cross the spinal cord stimulate alpha motor neurons in opposite limb = contract to support body weight
Structure voluntary movement
subcortical and cortical areas
association cortex
basal neclei
cerebellum
thalamus
motor cortex
motor units
Process leading to voluntary movement
initial drive to move
movement design ‘rough draft’
refined movement design
relay station
final executor of motor plan
execution of desired movement
Resting membrane potential why?
K+ intracellular (membrane more permeable) = diffuse out more
Na+ extracellular
= negative resting membrane potential
Grey matter
neurons
White matter
nerve axons
When is an action potential generated?
when an excitatory stimulus opens sodium channels
Movement plan
developed by motor cortex
sent to spinal centres for modification
Excitatory transmitters
neurotransmittrs that cause depolarization of membranes
