Dendrites: SMALL electrical messages
Axon: action potential LARGE electrical
between cells is
Dendrites: small electrical messages
Electrical messages can NOT cross synaptic cleft.
Signaling WITHIN one brain cell:
electrical (e.g. action potentials)
Signaling between most brain cells:
flow of signal
Nerve cells are signaling units for behavioural responses
Simple stretch reflex: knee jerk reflex
Example of a spinal reflex
(See page 150-151 of text book).
Tapping below patella, pulls on tendon and stretches muscle
Reflex contraction of quad muscle
Knee jerk reflex: monosynaptic circuit (1 synapse)
(sensory / motoneurons are directly connected)
Most spinal reflexes are polysynaptic (more than 1 synapse)
(Reflex networks can also can be modified by brain).
Plantar reflex: stroke foot – normal response is downward response
(curling in of toes)
Babinski response: upward with fanning of toes. Seen in infants
(up to ~ 2 yrs)
Infant reflex - hidden as we age (inhibited by cortex)
But can be unmasked by brain trauma, some diseases of
nervous system (or excessive alcohol)!
In Summary: 4 general features of the nervous system:
Stereotyped electrical signals (action potentials)
Connections (chemical synapses)
Specific connection patterns
Connections can be modified by experience
Ion channels in the nerve cell membrane
and neurotoxins that act on them.
The nerve cell membrane has ION CHANNELS (pores
that allow ions to move across the membrane)
In: From Neuron to Brain (4th Ed).
3 main properties:
1. Conduct ions...