Nerves Flashcards
Central Nervous System- components and function
1) Brain
2) Spinal
It processes information provided by a stimulus and provides a response
Peripheral Nervous System (2)
1- Somatic NS
2- Autonomic NS
Somatic NS
Pairs of nerves branching/ originating from the brain and spinal cord
Carry impulses from receptors to CNS (sensory) and CNS to effectors (motor)
Autonomic NS
Unconscious control of internal organs (heartbeat and breathing)
Stimulus
Detectable change in external or internal environment of an organism
Neurone and 3 types
Highly specialised cells that carry impulses in one direction. Neurones bundled together form nerves
1- Sensory
2- Relay
3- Motor
Sensory Neurone
Carries impulses from receptor cells to CNS (co-ordinator) via the dorsal root
Short and cell body in dorsal root ganglion
Relay neurone
Connector/ intermediate in CNS which connects sensory and motor neurones.
Receives impulse from sensory neurone and passes it onto the motor neurone.
Short and found in grey matter
Motor neurone + Effectors (2)
Carries impulses from CNS (co-ordinator) to the effector organs via ventral root to initiate a response. LONG
Effectors-
1- Muscle- contraction of muscle
2- Gland- secretion of hormone
Reflex action
Rapid/ fast, automatic and involuntary response to a stimulus, which is unconscious and does not involve the brain. Protective- prevents damage, harm and injury.
Reflex arc
Path travelled by impulses during reflex action.
Stimulus -> Receptor -> Sensory -> Relay -> Motor -> Effector -> Response
White and Grey matter
White- mainly axon and myelin and no cell bodies
Grey- darkly stained nuclei and cell bodies of neurones
Dendrite
Extensions that connect neighbouring neurones.
Carry impulses towards cell body
Axon
Slender/ long cytoplasmic extension which carries impulses away from the cell body
Cell body
Contains nucleus, rER, ribosomes to produce neurotransmitters and protein channels and mitochondria for ATP to carry impulse
Schwann Cells
Surround and support nerve fibres. Grow around axon to form the myelin sheath, which consists of many layers of phospholipid bilayers
Myelin sheath
Acts as electrical insulator around axon and speeds up transmission of impulses
Node of Ranvier
Areas where myelin sheath is missing, so the membrane can be depolarised in those regions
Axon terminal
Secretes neurotransmitter (synthesised in synaptic knob) to transmit impulse to adjacent neurone
Nerve nets
Simplest type of nervous system with 1 type of nerve cell. Short extensions joined and branched in different directions
- In jellyfish and hydra (invertebrates)
- Ganglion cells connect while sensory cells detect light and touch
- Hydra (radial symmetry) have simple pattern, easy to manipulate and regenerate fast
- Cannot detect direction of stimulus
- Hydra senses light and chemicals and responds with locomotion, hunt and feed
- Bigger intensity of stimulus = greater response
Nerve nets vs CNS
- It has 1 type of cell vs 3
- Non-myelinated vs myelinated
- Can transmit impulses in both directions
- Shorter neurones vs longer
- Slower transmission/ response vs faster transmission of impulses
- Small no of effectors vs greater no
- Respond to limited number of stimuli
- Impulse passes in all directions vs 1 direction
Why slower transmission in nerve nets?
- Non-myelinated so impulse has to travel across whole length of neurone/ axon
- In mammals, nodes/ myelin causes saltatory conduction which is faster as impulse jumps from node to node and not across entire length
