nervous system part 2

Spinal cord consists of two types of matter…

• white matter

• Gray matter

White matter

Typically broken down anatomically into posterior, lateral, and anterior horns and columns respectively

Superficial (in the spinal cord); contains myelinated and unmyelinated axons

Associated with the tracts that either project ascending information towards the brain or descending information towards the body

Gray matter

Typically broken down anatomically into posterior, lateral, and anterior horns and columns respectively

Surrounds the central canal; contains cell bodies, Neuroglia, and unmyelinated axons

Associated with sensory and motor nuclei; these nuclei are associated with the areas of the body they lie in close proximity to

Somatic afferent neurons

Sensory neurons that conduct impulses initiated in receptors in the skin, skeletal muscles, tendons, and joints

Visceral afferent neurons

Sensory neurons that conduct impulses initiated in receptors in smooth and cardiac muscle

Visceral efferent neurons

Motor neurons that conduct impulses to smooth and cardiac muscle, as well as glands

Somatic efferent neurons

Motor neurons that conduct impulses from the spinal cord to skeletal muscles

Corticospinal tract is…

responsible for sending motor information from the brain towards the muscles of the body

Neospinothalamic tract is responsible for…

Transmitting sensory information up towards the brain

Humunculi

The concept of the body within the brain

Spinal nerve

Formed by the union of ventral roots and dorsal roots

Ventral root

Contains axons of the motor neurons

Dorsal root

Contains axons of the sensory neurons

Is also associated with a ganglion

Ganglion

Cluster of cell bodies located in the peripheral nervous system

Spinal nerve distribution 1

Spinal nerve distribution 2

Spinal cord

Sends off to the following branches

• 8 vertical spinal nerve pairs

• 12 thoracic spinal nerve pairs

• 5 lumbar nerve pairs

• 5 sacral nerve pairs

• 1 coccygeal nerve pair

In the cervical region, the nerve comes out above the corresponding vertebrae

From the thoracic region to the coccygeal region, the nerve comes out below the corresponding vertebrae

Along the four areas of the spinal cord…

The ventral rami join into a plexus

Plexus

Branching network of nerves

1. Cervical plexus

2. Brachial plexus

3. Lumbar plexus

4. Sacral plexus

Cervical plexus

Includes ventral rami of C1-C5; innervates the neck, thoracic cavity, and diaphragm

Brachial plexus

Includes the ventral rami of C5-T1; serves to innervate the arm

Lumbar plexus

Includes ventral rami of T12-L4; helps innervate the thigh and leg

Sacral plexus

Includes the ventral rami of L4-S4; helps innervate the leg

Nerves of the leg

Dermatologist

Area of skin supplied by a single spinal nerve

• supplied b peripheral nerves

• Are stacked like discs in the thoracic and abdominal regions, yet run more longitudinally in the upper and lower extremities

Reflex

Involuntary and nearly instantaneous movement in response to a stimulus

They help test the integrity of the peripheral nervous system and/or central nervous system

Primitive reflexes are a special category of reflexes that are only found in human infants (babinski reflex)

Stretch reflex

Patellar reflex (hit the knee)

• called monosynaptic

• Checks integrity of dorsal root, spinal cord, and ventral root

Withdrawal reflex

Polysynaptic reflex

• have to do something to “excite” the inhibitors in order to create movement

Crossed extensor reflex

Babinski reflex and sign

(Pathological test)

• the curling of toes is healthy (flexor response)

• A baby doesn’t curl their toes due to them not walking yet (up to age 1)

  • Also called extensor response

• if an adult extends toes, something is not right with upper motor neuron

  • Very few ppl have paradoxical extensor response or no response at all

Automatic nervous system

Functions as a control system over the body’s internal organs and glands; influences heart rate, digestion, respiratory rate, salivation, perspiration, pupillary dilation, urination, sexual arousal, breathing and swallowing

Sympathetic nervous system

Involved with the “fight or flight” aspect of the ANS; sympathetic nerves originate inside of the vertebral column and extend from the first thoracic vertebral level down to second or third vertebral level; extensively involved with close proximity ganglia, which are cell bodies that reside in the peripheral nervous system

Parasympathetic nervous system

Involved with the “rest and digest” aspect on the ANS; parasympathetic nerves are either cranial nerves or are associated with sacral spinal nerves

Special senses

Intimately involved with the nervous system are as follows

1. Olfaction

2. Gustation

3. Vision

4. Balance

5. Hearing

pictured is the retina

Olfaction

Allows sense of smell, and begins the olfactory epithelium

Olfactory glands secret a mixture which coats the olfactory epithelium; the functions of this coat are unclear

Receptor cells

Highly modified neurons which can detect dissolved chemicals as they interact with odorant-binding proteins

Basal cells

Divide within the olfactory epithelium to replace worn out receptor cells

Gestation

Allows what is generally considered taste

The taste receptors, which are clustered into taste buds, are found on the tongue and pharynx

Taste sensations

1. Sweet

2. Salty

3. Bitter

4. Sour

5. Umami

Quenched thirst is also detected by water receptors

Three cases of lingual papillae

1. Circumvallate papilla

2. Fungi form papilla

3. Filiform papillae

Vision

Allows for what is commonly called sight

Light passes through a protective cornea, an anterior chamber, the lens of the eye, and a posterior cavity on its way to the retina

Retina cells react in response to light, sending nerve impulses towards the brain via the optic nerves (CN II)

Visions anterior chamber

Is filled with a fluid like substance called aqueous humor

Visions posterior chamber

Is filled with a clear, transparent, gelatinous mass called the vitreous humor

Rods

More numerous; have a high sensitivity to light; do not discriminate colors

Cones

Less numerous; most individuals possess three distinct types; make up the entirety of the fovea centralis

Macula lutes

Area near the center of the retina that contains closely packed photoreceptors for high acuity vision

Fovea centralis

Small indentation or put found in the central macula lutes; photoreceptors in this region are strictly cones

Optic disc

Allows ganglion cells to exit from the optic nerve; provides a passageway for the major blood vessels of the retina; due to the fact it is not associated with any rods or cones, each corresponds to a physiological blind spot

Focal point

Changes in the ciliary muscle help direct light onto the focal point of the retina for close distant vision

Myopia and hyperopia

Image formation

Balance and hearing

The cochlea associated with hearing

Balance is associated with the vestibule and semicircular canals

Vestibule

Encloses the saccule and utricle; responsible for detecting gravity and linear acceleration

Saccule

Detects movement in the vertical plane

Utricle

Detects movement in the horizontal plane

Semicircular ducts

Detects the rotation of the head