Nervous system Flashcards
Two types of coordinating system in humans
- Nervous system
- Endocrine system (hormones)
- These two work together.
Stimulus
- Any internal or external change
- To which an organism responds
Homeostasis
- Tendency to maintain a stable equilibrium between interdependent factors.
- Especially important for organisms that function within a specific range of conditions.
Nervous coordination
- Impulses conducted in nerves
- For rapid responses
Chemical coordination
- Hormones (chemical messengers) are transported in the blood
- Relatively slower responses
Two main systems of the human nervous system
- Central nervous system (CNS)
- Peripheral nervous system (PNS)
Generalised process of responding to stimuli
Stimulus -> detection -> processing and integration -> response
How a stimulus is detected
Receptors detect stimuli and convert them into nerve impulses
How a response is actioned
Effectors (muscles and glands)
Components of nervous tissue
- Nerve cells called neurons
- Connective tissue called neuroglia
Main parts of a neuron
- Dendrites
- Cell body (cytoplasm and nucleus)
- Axon (with myelin sheath)
- Terminal branches of axon (synaptic knobs)
Dendrites
- Conduct impulses to the cell body
- One or more dendrites may be present in a neuron
Axons
- Carry nerve impulses away from the cell body
- Forms a number of terminal branches
- Synaptic knobs at the tips
Myelin sheath
- Nerve fibres outside CNS enclosed by myelin
- Insulates the nerve fibres and accelerating impulse transmission
- Formed by specialised Schwann cells
- these wrap spirally around nerve fibres
- myelin is a white fatty protein found in the cell membrane
Nodes of Ranvier
- Gaps in the myelin sheath between Schwann cells
- Speed up transmission as impulses jump from one node to another
Neurilemma
- Outermost membrane of myelin sheath
- Assist in repairing and regenerating damaged PNS neurons
- (unmyelinated fibres and axons of the CNS cannot regenerate or be repaired)
Neuron structural classification
Depends on number of outgrowths from cell body:
- Multipolar (more than two)
- Bipolar (two)
- Unipolar (one)
Neuron functional classification
- Sensory (afferent) neurons - impulses from receptor to CNS
- Motor (efferent) neurons - impulses from CNS to effectors
- interneurons (connector neurons) - neurons of the CNS
Synapse
The gap between an an axons synaptic knob and a dendrite
How an impulse crosses a synapse
- neurotransmitter chemicals
- e.g. serotonin
Where neurotransmitters are formed and how they are released
- synaptic vesicles alongside many mitochondria providing required energy
- Impulses cause the vesicles to burst at the surface of the pre-synaptic membrane
- The neurotransmitter is released into the synaptic cleft
How the nerotransmitter passes on an impulse to the dendrite.
- The neurotransmitter moves across the synaptic cleft
- It attaches to the post-synaptic membrane
- This generates electric signals that are conducted as nerve impulses to the cell body of the next neuron
The significance of a synapse
- Signals only move in one direction
- Impulses can be transmitted to many neurons, afecting more than one effector
- Insignificant stimuli can be filtered out
- The synapse filters out weak signals, preventing overloading of the CNS
