Sensory nerve tracts in spinal cord
Neurons that transmit impulse towards brain are called sensory (afferent, ascending).
Two main sources of sensation transmitted to brain via spinal cord.
a.Skin,
b. tendons, muscles and joints
1. Skin
Sensory receptors (nerve ending) in skin called cutaneous receptors, are stimulated by pain, heat, cold, touch, pressure.
Nerve impulse generated are conducted by neurons to sensory area in opposite hemisphere of cerebrum where sensation and its location are percieved.
Crossing to other side or decussation occurs either at the level of entry into cord or in medulla but this crossing will not effect the motor action.
2. The tendons, muscles and joints
Sensory receptors are specialized nerve ending in these structures, called proprioceptors, and they are stimulated by stretch.
Motor nerve tracts in spinal cord
Neurons that transmit nerve impulses away from brain are motor (efferent, descending) neuron.
Motor neuron stimulation result in-
1. Contraction of skeletal (voluntary) muscle
2. Contraction in smooth (involuntary) muscle, cardiac muscle, secretory gland
1. Voluntary muscle movement
Contraction of muscles that move joints is under voluntary control, which means that stimulate to contract originates at level of consciousness in cerebrum. However some nerve impulse that effect skeletal muscle contraction are mid brain, brain stem and cerebellum.
This involuntary activity is associated with coordination of muscle activity, movement, maintenance of posture and balance, eye blinking.
2. Involuntary muscle movement
These have their cell bodies in brain at level below cerebrum i.e in mid brain, brain stem, cerebellum or spinal cord.
They influence muscle activity that maintains posture and balance coordinates skeletal muscle movement and control muscle tone.
Primary motor area in cerebrum; upper motor neurons to lower motor, travel nerve impulse to skeletal muscle.
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