Nervous system Flashcards
What is the CNS?
Comprised of brain and spinal cord and protected by meninges (protective membrane)
What is the PNS?
Comprised of the somatic nervous system
What is a nerve net?
Consists of short, unmyelinated, relatively slow nerve cells
What is meninges?
Tough protective membrane which surrounds brain and spinal cords
What is the order of the relay, motor and sensory neurones?
Sensory - Relay - Motor
What is the sensory neurone?
Carry nerve impulse from receptor cell to coordinator, either the brain or spinal cord
What is the relay neurone?
Lies in CNS. Receives impulse from sensory and passes to motor neurone
What is the motor neurone?
Carry impulse from coordinator to effector (muscle or glands)
What are dendrons?
Part of axon between the dendrites and the cell body
What are dendrites?
Thin extensions that carry the impulse towards cell body
What are axons?
Long cytoplasmic extensions which transmit impulse away from cell body
What is the role of the receptor?
To detect the stimulus
What is the role of the effector?
The muscle or gland which carries out the response
What is the myelin sheath?
Many Schwann cells that form a multi-layered fatty sheath to speed up impulse
What are Schwann cells?
Cells which surround and insulate neurones
What are Nodes of Ranvier?
Areas along axon where myelin sheath is missing
What is grey matter?
Contains the neuronal cell bodies and unmyelinated neurones
What is a dorsal root ganglion?
Area of spinal cord where cell bodies of sensory neurones are found
What is a ventral root?
Area of spinal cord where the motor neurone exits
What is the cell body?
Part of nucleus which contains the nucleus, RER, numerous mitochondria and other organelles
What are the differences between Hydra and humans?
Hydra: Doesn’t have a CNS, has a nerve net. 1 type of nerve cell. Short cell process. No myelin insulation. Slow conduction speed. Impulse from point of stimulation travel both directions. Few effectors. Few stimuli that can be detected by sensory receptors
Humans: Has CNS. Contains 3 types of nerve cell (sensory, relay, motor). Long cell process. Has myelin insulation. Fast conduction speed. Many effectors. Lots of stimuli that can be detected by sensory receptors
What is the length of a sensory neurone?
Short
What is the length of a relay neurone?
Short
What is the length of a motor neurone?
Long
Where are sensory neurones found?
Dorsal root ganglion
Where are relay neurones and motor neurones found?
Grey matter
What is the end of an axon called?
Axon terminal, synaptic endings
Where does the impulse start from?
Dendrons
What is a reflex arc?
A reflex arc is the neural pathway that controls an involuntary response to a stimulus
What is the order of a reflex arc?
Receptor –> Sensory neurone –> (through dorsal root and past dorsal root ganglion (cell body)) –> Relay neurone –> Motor neurone –> (through ventral root) –> Muscle/gland/effector
What does grey matter contain?
Many cell bodies
What does white matter contain?
Many axons
What is in the middle of the grey matter?
Central canal
What is a reflex action?
An action that takes place involuntarily to avoid injury or damage
What is the first stage of an action potential?
Resting potential: The Na+/K+ pump actively transports 3Na+ ions out and 2K+ ions into axon. High conc of Na+ out and high conc of K+ in axon. As the K+ channel is always open, some diffuse back out down the conc gradient. Therefore membrane becomes polarised and axon is negative as less + ions inside. -70mV.
What is the second stage of an action potential?
Depolarisation: An action potential (stimulation) occurs and causes the voltage to go from -70mV to +40mV. Na+ diffuses into axon down a concentration gradient due to the Na+ voltage gated channels being open. Membrane is now depolarised. +40mV
What is the third stage of an action potential?
Repolarisation and hyperpolarisation (refractory period): Voltage gated K+ channels open and K+ diffuses out of axon. Membrane repolarised as + charge decreases in the axon. Excessive decrease in charge due to many K+ leaving axon results in hyperpolarisation. -90mV
What is the fourth stage of an action potential?
Resting potential: Voltage gated K+ channels close. Na+/K+ pump restarts and restores resting potential. Membrane polarised
What is a refractory period?
Na+ channels deactivated for a short time which prevents an action potential in the opposite direction and a second potential being generated too close to the first one
What factors effect the speed of conduction of the nerve impulse?
Myelination, diameter of axon, temperature
How does myelination effect the speed of nerve impulse?
Insulates axon, depolarisation and action potentials only occur at the Nodes of Ranvier. The impulse jumps from one node to the next which speed up the impulse. Called SALTATORY CONDUCTION
How does diameter of axon effect the speed of nerve impulse?
Greater diameter = lower resistance to ion flow and a greater speed of transmission
How does temperature effect the speed of nerve impulse?
Up to 40 degrees, greater speed of transmission as involves active transport and requires ATP from respiration. Anything that speeds up respiration rate also speeds up transmission
How does transmission over a synapse occur?
Action potential arrives at axon terminal (pre-synaptic knob)
Calcium ions flood into the pre-synaptic knob via diffusion as more concentrated outside of axon
Calcium ions cause vesicles to move towards pre-synaptic membrane where they fuse and release acetylcholine into the synaptic cleft (exocytosis)
Acetylcholine molecules diffuse across cleft to post-synaptic membrane and bind to receptors
Ligand gated Na+ channels open and Na+ diffuses into dendrite of post-synaptic membrane creating an action potential (depolarisation)
Acetylcholine broken down by cholinesterase into choline and acetate and the ligand gated Na+ channels close
Choline and acetate diffuse back to pre-synaptic membrane and resynthesized into acetylcholine
Energy from mitochondria puts acetylcholine back into vesicles
What are excitatory drugs?
Drugs that increase number of action potentials in post-synaptic neurone e.g. organophosphates inhibit acetylcholinesterase so acetylcholine isn’t broken down and continues to stimulate receptors
What are inhibitory drugs?
Drugs which decrease the number of action potentials within a post-synaptic membrane e.g. Botox prevents release of acetylcholine from vesicles so receptors aren’t stimulated
What is an agonist in the body?
A substance which fits into a receptor and stimulates it
What is an antagonist in the body?
A substance which fits into a receptor but doesn’t stimulate it
What are stimulants?
Drugs that perk you up e.g. caffeine
What are depressants?
Drugs that knock you down e.g. alcohol
What is temporal summation?
A post-synaptic neurone may only be stimulated if there are frequent action potentials in the pre-synaptic neurone
What is spatial summation?
A post-synaptic neurone may only be stimulated if several pre-synaptic neurones receive stimulation
