Lecture 5 16th February 2017
Neural Circuits
Circuits of the spinal cord
Physiological Functions of spinal cord circuits:
Initial processing of somatosensory (afferent) input by the CNS
Final processing of motor (efferent) output by the CNS
Spinal nerves are highways of both somatosensory information traffic to the
spinal cord (afferent pathways) and motor information traffic from the spinal
cord to the muscles (efferent pathways)
The somatosensory system includes multiple types of sensation from the body
- light touch, pain, pressure, temperature, and joint and muscle position sense
(also called proprioception).
Sensation:
Detection by receptors
Perception:
Interpretation by spinal cord and brain circuits
Receptors are:
Neurons specialised in the transduction of energy generated by external
stimuli
Specific for a narrow range of input
Neurons in sensory systems signal events by a combination of rate, spatial and
temporal codes
Rate code
Frequency of APs
Spatial code
Summation of APs from multiple neurons
Temporal code
Timing of APs
Convergence and divergence
High spatial resolution required: low convergence (e.g., cones
and bipolar cells in retina). This allows us to see in high
resolution
Detection of weak signals required: high convergence(e.g., rods
and bipolar cells in the retina). As you need to amplify weak
signals in the environment
Input is used for complex or multiple functions: high divergence
(e.g., vestibulo-ocular reflex).
Neural Circuits
Circuits of the spinal cord
Physiological Functions of spinal cord circuits:
Initial processing of somatosensory (afferent) input by the CNS
Final processing of motor (efferent) output by the CNS
Spinal nerves are highways of both somatosensory information traffic to the
spinal cord (afferent pathways) and motor information traffic from the spinal
cord to the muscles (efferent pathways)
The somatosensory system includes multiple types of sensation from the body
- light touch, pain, pressure, temperature, and joint and muscle position sense
(also called proprioception).
Sensation:
Detection by receptors
Perception:
Interpretation by spinal cord and brain circuits
Receptors are:
Neurons specialised in the transduction of energy generated by external
stimuli
Specific for a narrow range of input
Neurons in sensory systems signal events by a combination of rate, spatial and
temporal codes
Rate code
Frequency of APs
Spatial code
Summation of APs from multiple neurons
Temporal code
Timing of APs
Convergence and divergence
High spatial resolution required: low convergence (e.g., cones
and bipolar cells in retina). This allows us to see in high
resolution
Detection of weak signals required: high convergence(e.g., rods
and bipolar cells in the retina). As you need to amplify weak
signals in the environment
Input is used for complex or multiple functions: high divergence
(e.g., vestibulo-ocular reflex).
