31 pairs; mixed nerves. Cervical (C1-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5) and coccygeal. Connective tissue coverings of spinal nerves: Epineurium, perineurium and endoneurium: Fascicles
Spinal nerves branch and their braches are called rami: Posterior (dorsal) ramus Anterior (ventral) ramus Plexuses: a network of axons Anterior rami except T1-T11 form plexuses.
Formed by the anterior rami of C1-C5. Phrenic nerves- important nerves from the cervical plexuses.
Formed by the anterior rami of C5-C8 & T1.Supplies the shoulders and upper limbs.Roots → trunks → divisions → cords → nerves.
Important nerves that arise from the brachial plexuses are Axillary nerve Musculocutaneous nerve Radial nerve Median nerve Ulnar nerve
Formed by the anterior rami of L1-L4. Supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs. Femoral nerves, obturator nerves.
Formed by the anterior rami of L4-L5 and S1-S4. Supplies the buttocks, perineum, and lower limbs. Gives rise to the largest nerve in the body- the sciatic nerve.
Formed by the anterior rami of S4-S5 and the coccygeal nerves. Supplies a small area of skin in the coccygeal region.
Dermatome is the area of the skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal nerve.
The name of the tract often indicates its location in the white matter and where it begins and ends. The white matter contains both sensory and motor tracts.
A reflex is an automatic, sudden, involuntary response to a stimulus. When the integration takes place in the spinal cord, the reflex is a spinal reflex.
The pathway followed by nerve impulses that produce a reflex is a reflex arc. A reflex arc includes: a. sensory receptor b. sensory neuron c. integrating center d. motor neuron e. effector
1
SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential)
1
SENSORY NEURON (axon conducts impulses from receptor to integrating center)
SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential)
2
1
SENSORY NEURON (axon conducts impulses from receptor to integrating center)
SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential)
INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons)
Interneuron
2
3
1
SENSORY NEURON (axon conducts impulses from receptor to integrating center)
SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential)
INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons)
MOTOR NEURON (axon conducts impulses from integrating center to effector)
Interneuron
2
3
4
1
SENSORY NEURON (axon conducts impulses from receptor to integrating center)
SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential)
INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons)
MOTOR NEURON (axon conducts impulses from integrating center to effector)
EFFECTOR (muscle or gland that responds to motor nerve impulses)
Interneuron
2
3
4
5
Causes contraction of a skeletal muscle in response to stretching of the muscle.Monosynaptic reflex.Patellar or knee-jerk reflex: Stretching of a muscle →activation of muscle spindles →sensory neuron →spinal cord→motor neuron → muscle contraction.Ipsilateral.
1
Stretching stimulates SENSORY RECEPTOR (muscle spindle)
Antagonistic muscles relax
1
Stretching stimulates SENSORY RECEPTOR (muscle spindle)
SENSORY NEURON excited
To brain
Spinal Nerve
+
+
2
1
Stretching stimulates SENSORY RECEPTOR (muscle spindle)
SENSORY NEURON excited
Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron
Inhibitory interneuron
To brain
Spinal Nerve
+
– +
2
3
1
Stretching stimulates SENSORY RECEPTOR (muscle spindle)
SENSORY NEURON excited
MOTOR NEURON excited
Antagonistic muscles relax
Motor neuron to antagonistic muscles is inhibited
Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron
Inhibitory interneuron
To brain
Spinal Nerve
+
– +
+
2
3
4
1
Stretching stimulates SENSORY RECEPTOR (muscle spindle)
SENSORY NEURON excited
MOTOR NEURON excited
EFFECTOR (same muscle) contracts and relieves the stretching
Antagonistic muscles relax
Motor neuron to antagonistic muscles is inhibited
Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron
Inhibitory interneuron
To brain
Spinal Nerve
+
– +
+
2
3
4
5