The Nervous System Flashcards
Define stimulus
- a change in environment that triggers a reaction (response)
- organism responds in way that benefits itself
Define Response
- organism reaction to stimulus
Define sensitivity
- ability of organism to detect and respond to changes in environment
- survival dependent on appropriate response to stimuli
Role of nervous system
- control activities of body and how it reacts to stimuli
- transmit info as nerve signals
- senses stimuli in surroundings, determines and directs responses to surroundings
- enable coordination of diff parts of body
- consist of well-developed brain, spinal cord, spianl nerves, highly specialised sense organs
Define involuntary actions
- automatic activities
- not controlled consciously
Define voluntary actions
- activities that are controlled consciously
Voluntary actions (e.g. patting cat) Nervous pathway
- cat rubs against leg (stimuli)
- touch receptors at leg stimulated
- nerve impulses transmitted thru sensory neurones to spinal cord
- relay neurones conduct nerve impulses to brain
- brain evaluates info, decides response (pat cat)
- brain generate nerve impulses
- nerve impulses transmitted along relay neurones to motor neurones
- impulses transmitted to effector muscles (causes contraction of arm muscles, pat cat)
Sense organs
- help body adjust quickly to stimuli
2. enable various parts of body to coordinate quickly
Central Nervous System (CNS)
- brain
- spinal cord
- integrate and process impulses received frm PNS
Peripheral Nervous System (PNS)
- cranial nerves
- spinal nerves
- provide comm link between CNS and other parts body
How does nervous system process info? (nervous pathway)
- info gathered by receptors (sense organs)
- info converted to electrical signals (nerve impulses)
- nerve impulses transmitted by peripheral nerves to CNS
- brain process info based on pattern of impulses
- sends nerve impulses to effectors (muscle/glands)
- intended action carried out
Nervous tissue (neurones)
- consist of 3 types of nerve cells (neurones)
- sensory, relay, motor neurones
Basic structure of neurone
- cell body (nucleus, cytoplasm)
- axon
- dendron
- dendrites
Cell body
- 1 nucleus and cytoplasm
- mitochondria and ribosomes present
- metabolic activities carried out
Dendron
- receives info
- nerve fibres (conduct impulses towards cell body)
- small, break up into terminal branches (dendrites)
Dendrites
- many short branching processes frm dendron (increase SA:V, faster transmission rate)
- specialised in receiving excitation, stimuli, impulses frm another neurone, conducting impulses towards cell body
Axon
- long nerve fibre, sometimes branced (may rch more than 1m)
- 1 axon per neurone
- diameter frm 0.5mm (increase SA:V)
- conduct impulse from dendrites, away frm cell body to synapse
Structure of motor neurone (Dendron, dendrites, axon)
- Dendron: nerve fibres that transmit nerve impulses towards cell body
- Dendrites: receive nerve impulses frm other neurones
- Axon: nerve fibres that carry impulses away frm cell body, ends of axon transmit nerve impulses to effector
- Pathway: dendrites, dendron, cell body, axon, effectors
Nodes of Ranvier
- regions where myelin sheath is absent on cell fibre
- speed up transmission of impulses (allow them to jump frm node to node)
Myelin sheath
- layer of fatty substance
- shields and insulates nerve fibre
- surrounded by neurilemma (thin membrane)
- ensures impulse isn’t lost (lesser needs to be generated)
Motor end plate
junction between axon terminal and muscle fibre
What happens if Myelin Sheath is damaged?
-some glands won’t work, muscles might not contract (may lead to paralysis)
Sensory neurone
- found between sensory receptors and CNS
- transmit nerve impulse frm sense organs to CNS
- pathway: Dendrites, dendron (towards cell body in middle of neurone), axon, relay neurone in CNS
Diff between sensory and motor neurone (3)
- S: long dendron, short axon ; M: short dendron, long axon
- S: circular cell body ; M: irregular shaped cell body
- S: conducts nerve impulse frm sensory receptors to CNS ; M: conducts impulse frm CNS to effectors
Synapse
- junction/connection between 2 neurones
- impulses transmitted frm axon to dendron across a synapse
- transmission across synapse is via chemical means (thru transmission of neurotransmitters in synaptic vesicles)
Define nerves
- bundle of nerve fibres bundled in sheath of connective tissue
- cranial nerves: nerves frm brain
- spinal nerves: nerve frm spinal cord, mixed fibres (sensory and motor nerve fibres)
Grey matter
- contains cell bodies of neurones
- found at outer layer of brain, central parts of spinal cord
White matter
- contains mainly nerve fibres of neurones
- found in central part of brain, outer layer of spinal cord
Spinal cord and spinal nerves
- spinal cord encased in vertebral column
- spinal nerves emerge frm spinal cord (31 pairs)
- grey matter in central part of spinal cord “H” shape
- known as central canal, contains cerebrospinal fluid (runs thru middle of spinal cord)
Spinal nerve (dorsal and ventral roots)
- each spinal nerve divides into 2 roots
- subdivides into branches, supply nerve fibres to various parts of body
- dorsal (top)root: contain only sensory neurones
- dorsal root ganglion: cluster of sensory neurones (bulge)
- ventral (bottom) root: contains only motor neurones
Relay neurones (nerve impulse transmission)
- relay neurones lie within grey matter of spinal cord
- transmit nerve impulses from sensory neurones to brain; brain to motor neurones; sensory neurones to motor neurones (reflex)
- relay neurones form synapses with sensory and motor neurones
