Recents in Beach

SPINAL CORD- CTEVT Spinal Cord Notes

SPINAL CORD- CTEVT Spinal Cord Notes

SPINAL CORD: The spinal cord is an elongated, cylindrical nervous structure which continues below medulla oblongata.
It is suspended in the vertebral canal, surrounded by meninges and CSF.
It is 45 cm long.
It extends from the upper border of the atlas(C1) to lower border of first lumbar vertebra(L1). Its
lower tapering extremity is called conus medullaris. The apex of conus medullaris continues
downward as a thin, thread-like filament called filum terminale. Nerve fibres form a bunch around
filum terminale called cauda equina because of its resemblance to the tail of a horse. (CTEVT)
The spinal cord is made up of 31 spinal segments: cervical-8, thoracic-12, lumbar-5, sacrum-5 and
coccyx-1.


Internal structure of spinal cord: (CTEVT)

The spinal cord is incompletely divided into two parts, anteriorly by anterior median fissure and
posteriorly by a posterior median septum. It consists of grey matter in the centre surrounded peripherally by white matter.
Grey matter: it is central H shaped(butterfly) part. It has an anterior, posterior and lateral horn. Centrally it is pierced by the central canal.
White matter: it is a peripheral part except for the H shaped area. It also consists of anterior, posterior and lateral columns.
Tracts of the spinal cord are collections of nerve fibres within CNS. The tracts are sensory ascending to the brain, motor descending from the brain and connector type.
The descending tracts are either named as corticospinal (pyramidal) or extrapyramidal.
 

Functions of tracts of the spinal cord:
a.Ascending tracts



Fig. 1
Spinal Cord
Spinal Cord Fig. 2
b.Descending Tracts

REFLEX ARC: *CTEVT

The basic unit of integrated reflex activity is called the reflex arc.
It consists of five components:

 a) receptor 
b) sensory neuron
c) interneuron 
d) motor neuron
e) effector

a. Receptor/sensory organ:

Located within the skin, a tendon, a joint, or some other peripheral
organ, a receptor consists of dendritic endings of a sensory neuron that responds to specific stimuli,
such as sudden pressure or pain.



b. Sensory neuron/afferent neuron: 

Extending from the receptor through the posterior root, the
sensory (afferent) neuron conveys stimuli to the posterior horn of the spinal cord. The cell bodies of
sensory neurons are located in posterior root ganglia.



c. Center:  

The axon of sensory neuron synapses with an association neuron (also called an
interneuron or internuncial neuron) within the center.



d. Motor neuron/efferent neuron: 

Beginning at a synapse with the association neuron, the motor
neuron conveys impulses from the anterior horn of the spinal cord, through the anterior root, to the
effector organ.
 

e. Effector: 

The effector is a muscle or gland that responds to a motor impulse by contracting or
secreting, respectively.
Effector
Fig. Effector


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