chapter 13 nervous system Flashcards
what are the 3 types of neurones
Sensory neurones: detects stimulus, generates and transmits nerve impulses from sense organs/receptors to CNS
Relay neurones: found within CNS = transmits nerve impulses from sensory neurones to motor neurones
Motor neurones: transmits impulses from CNS to effectors to take action
role of spinal cord
to relay messages (responses) from the brain to different parts of the body (effector i.e. muscle) in order to perform an action;
→ to pass along messages from sensory neurones to the brain (in a voluntary action)
→ to coordinate reflexes to elicit immediate responses to a specific stimuli without conscious control (reflex action)
parts of sensory/motor neurone and their functions (7)
- Cell body: contains nucleus, cytoplasm, cell surface membrane and organelles
- Dendron: transmit nerve impulses (from dendrites) towards cell body
- Dendrites: receive nerve impulses from other neurones
- Axon: transmits nerve impulses away from cell body
- Myelin sheath: membrane/layer to insulate the axon from the electrical impulses transmitted along the neurone (prevent impulses from ‘escaping’)
- Nodes of Ranvier (where myelin sheath is absent): speed up transmission by allowing impulses to jump from node to node (eg instead of going straight, can just jump)
- Axon terminal: where nerve impulses are transmitted from neurones to other neurones
(eg motor neurones to effector → would be located in the effector muscle (for MN)
differences in sensory and motor neurone
shape of cell body: circular in sensory neurone but irregular in motor neurone
axon length: short in sensory neurones but long i motor neurones
dendron length: long in sensory neurones but short in motor neurones
what affects speed of transmission (3)
- Diameter of axon: the larger the diameter of an axon, the faster the speed of transmission = resistance is inversely proportional to the cross-sectional area of an axon
- Presence of myelin sheath: a thicker layer of myelin sheath insulates better = confine (‘not letting the impulses escape to other neurones’) the impulses within = quickens the propagation (transmission) of the impulse along the axon
- Temperature: increase in temperature = increases the conduction speed of impulses along neurone
what is white and grey matter
–> grey matter: cell bodies of motor and relay neurones
Brain: outer part
Spinal cord: inner part (shaped like H)
→ white matter: nerve fibres of sensory and motor neurones
Brain: inner part
Spinal cord: outer part
parts of spinal cord
what is voluntary action and its pathway
→ a voluntary action is a conscious, deliberate action: involves the brain making a decision (even if the action is not occurring near the brain)
→ voluntary action comes with a sensation
→ pathway: interpreting impulse in forebrain - relay neurone (in white matter of spinal cord) - motor neurone (in grey matter of spinal cord) - effector
example of sensation
SENSATION
1. movement of a cat against leg (stimuli) was detected by the photoreceptors in retina of eye
photoreceptors produce nerve impulses =
2. transmitted along the sensory neurones in the optic nerve to the relay neurones in the spinal cord
3. nerve impulses are transmitted from the relay neurones in spinal cord to the brain
4. Forebrain interprets impulses = Person feels the sensation of the cat eg the soft fur against leg
example of voluntary action
ACTION
1. Forebrain comes up with a response (eg petting the cat) = nerve impulses are transmitted from the brain through relay neurones in (white matter of) spinal cord
2. Nerve impulses are transmitted to motor neurones (in grey matter of SC) then to the effector, muscles in the hand
3. Muscles in the hand contract, causing the hand to pet the cat
what is reflex action + reflex arc
an involuntary action is an immediate response to a specific stimulus without conscious control - controlled by reflex centres closest to stimulus: spinal cord and brain (but not consciously)
require a reflex arc: the shortest pathway where nerve impulses travel from the receptor to effector in a reflex action to elicit an immediate response to a specific stimulus without conscious control
Pathway: (stimulus) → receptor - sensory neurone (in dorsal root) - relay neurone in grey matter of reflex centre - motor neurone (in ventral root) - effector (muscles/gland)
describe knee jerk reflex
- Stimulus for knee-jerk reflex is the sudden tapping below the kneecap;
- Stretch receptor on the knee detects stimulus = generates nerve impulses;
- Nerve impulses transmitted along the sensory neurone to the relay neurone in CNS in spinal cord (grey matter of spinal cord)
- Nerve impulses transmitted from the relay neurone of (grey matter of spinal cord) CNS in spinal cord to the motor neurone
- Nerve impulses transmitted along the motor neurone to the effectors, upper thigh muscles;
- Upper thigh muscles contract causing the leg to move forward/momentary kicking action
what happens when sensory neurone is damaged
- Lower limbs able to move consciously: Nerve impulses can still be transmitted btwn brain to effector muscles by motor neurones
- No sense of feeling in limbs: Nerve impulses generated by receptor cannot be transmitted to brain since sensory neurone is damaged
what happens when motor neurone is damaged
- Able to feel sensation in limbs: Nerve impulses generated at receptor can be transmitted to brain = interpreted to give sensation
- Limbs unable to move: Nerve impulses cannot be transmitted from CNS to effector since motor neurone is damaged
what happens when relay neurone is damaged
- Able to move but involuntarily: Nerve impulses generated at receptor can travel to effector via reflex arc to produce a response
- Unable to feel anything: Nerve impulses cannot be transmitted to brain as RN is damaged = no sensation felt
