Central - , Spinal & Spinal Reflexes

Chapter 13A

Central nervous system (CNS) is responsible for: Receiving impulses from receptors Integrating information Sending impulses to the effectors

It is composed of: Spinal cord Spinal Cord - Functions

Spinal cord has the following functions: 1. Receive and send impulses: receives impulses from receptors and sends impulses to the effectors.

2. Communication with the brain: has bundles/cables of fibers (tracts) that take sensory impulses up to the brain or motor impulses down from the brain.

3. Movement: muscle contraction for basic movement is controlled by the spinal cord…although the initiation, the speed and the direction of movement is controlled by the brain.

4. Reflexes: simple reflexes are controlled by the spinal cord….pulling your finger back when you touch a hot plate. Complex reflexes are controlled by the brain… remembering not to touch a hot plate again! Spinal Cord - Protection

Meninges Spinal cord

Meninges

Vertebra

Vertebral foramen

Spinal cord is protected by bones and 3 membranes called meninges. From outside  inside: 1. Boney protection: vertebrae  vertebral foramina align  form vertebral canal  houses spinal cord. 2. Dura mater: outermost tougher meninx. 3. Arachnoid mater: middle avascular meninx. 4. Pia mater: innermost meninx that sticks to the spinal cord. Spinal Cord –Spaces

There are spaces between the protective bones and the 3 meninges.

1. – space between vertebrae and the dura mater- filled with adipose tissue.

2. –space between dura mater and arachnoid-filled with interstitial fluid (no such space in healthy person; space appears when there is trauma or underlying pathological conditions).

3. Subarachnoid space – space between arachnoid and pia mater- filled with (CSF). Spinal Cord /spinal tap

Lumbar puncture/Spinal tap: a sample of CSF is removed from subarachnoid space  chemical analysis for diagnosis of certain diseases and disorders- like , Multiple Sclerosis, CNS tumors etc..

Epidural : an anesthetic shot given in the epidural space of lumbar region  numbs specific spinal nerves in the immediate area of injection…usually used for child birth, in the pelvic region and legs.

Meningitis: inflammation of meninges…bacterial or viral. If left untreated  spreads to brain  death.

Spina bifida: incomplete closure of the pedicles of the vertebrae  spinal cord and nerves not well protected  paralysis of lower extremities and pelvic organs….May be due to lack of vitamin B/folic acid during pregnancy. Spinal Cord – External Structure

During early childhood development, and spinal cord grow.

Around age 4 or 5 years, spinal cord growth slows down while vertebral column continues to grow.

Therefore in an adult, spinal cord extends from the base of the brain  ends at L1 or L2. Termination of pinalS Cord The level of the spinal cord segments do not relate exactly to the level of the vertebral bodies i.e. damage to the bone at a particular level e.g. L5 vertebrae does not necessarily mean damage to the spinal cord at the same level. Spinal Cord – External Structure

Spinal cord is not uniform along its length. The amount of gray matter is greatest in segments of spinal cord dedicated to the sensory & motor control of the limbs.

Two regions of the spinal cord are wider: : located in the cervical and upper shoulder region  supplies nerves to the shoulder and upper limbs.

Lumbar enlargement: located in the thoracic region  innervates pelvis and lower limbs.

Conus medularis: tapered, cone shaped ending of the Termination spinal cord. of pinalS Cord Located in L1-L2 region.

Cauda equina: A group of nerves that originate from the  includes lumbar (2nd-5th), L1 sacral (1st to 5th) and coccygeal (1) spinal nerves. L2 - Resemble horse’s tail. L3 L4 - Function:- send and receive messages between the L5 lower limbs and the pelvic organs, which consist of the bladder, the rectum, and the internal genital organs. Spinal Cord – Anchoring

Pia mater Arachnoid Dura mater

Spinal cord is located inside the vertebral canal. It needs to be anchored to prevent it from moving around: : extension of pia mater from conus medullaris  to anchor spinal cord down to the coccyx. Denticulate ligament: extensions of pia mater-attaches laterally to arachnoid and dura mater-stabilizes side-to-side movement of spinal cord within vertebral column. Spinal Cord – Internal Structure

Anterior or Posterior?? Posterior/dorsal

Anterior/ Posterior/ Ventral dorsal

Anterior or Posterior?? Anterior/ventral

To understand the internal structure of the spinal cord…..you have to get the directions right!!!! Here you see spinal cord inside a . Which side is anterior and which is posterior?? Spinal Cord – Internal Structure

Posterior/dorsal side Posterior median

White matter

Gray matter Anterior median fissure

Anterior/ventral side Superior view

Anterior median fissure: a deep groove that runs along the anterior surface of the spinal cord. Posterior median sulcus: a depression that runs along the posterior surface of the spinal cord. The tissue can be divided into gray matter and . Gray matter: in the shape of letter H….towards the center. White matter: around the gray matter….along the periphery. Spinal Cord – Internal Structure- Gray matter

Central canal

Gray commissure

Gray matter:- dominated by the cell bodies of , neuroglia, and unmyelinated , surrounds the narrow and forms a butterfly shape or letter H shape.

Horns:- the projections of gray matter toward the outer surface of the spinal cord 2 arms of the letter H.

Gray commissure- the cross bar that connects the gray horns/middle portion of the gray matter.

Central canal: located in the center of the gray commissure  has CSF  lined by ciliated ependymal cells to circulate CSF. Spinal Cord – Internal Structure- Gray matter

Posterior/Dorsal Posterior side gray horn Posterior/Dorsal gray horn: posterior part of gray matter Function: contains sensory nuclei- somatic and visceral - receives information from skeletal muscles and skin (somatic) and visceral organs (visceral) and relays it to CNS. Anterior side

Dorsal root Posterior side : contains the cell bodies of sensory neurons whose axons carry information to the spinal cord.

Anterior side

Dorsal root Posterior side

Dorsal root: contains the axons of the sensory neurons whose cell bodies are in the dorsal root ganglion.

Anterior side

What structure is within the dorsal root ganglion? Cell bodies of sensory neurons Spinal Cord – Internal Structure- Gray matter

Posterior side Anterior/Ventral gray horn: anterior part of gray matter Function: contains motor nuclei (somatic) –sends commands to skeletal muscles. Anterior/Ventral Anterior side gray horn

Posterior side Ventral root: connected to ventral horns of spinal cord Contains axons of motor neurons send message out to effectors

Anterior side Ventral root

Posterior side Lateral gray horn: lateral side of gray matter Function: contains visceral motor nuclei –sends commands to smooth muscle, cardiac muscle and glands.

Anterior side Lateral gray horn

What types of neurons travel through the dorsal root? Sensory neurons What types of neurons travel through the ventral root? Motor neurons A single spinal nerve contains the axons of BOTH sensory and motor neurons. The sensory fibers enter the CNS through the dorsal root. The motor fibers emerge from the CNS via the ventral root. Spinal Cord – Internal Structure- White matter

Posterior median sulcus Posterior white column Lateral white column

Posterior/ dorsal horn Anterior white column

The superficial white matter contains large numbers of myelinated and unmyelinated axons. The structural components of white mater are divided into columns.

1. The posterior white column- lies between the posterior gray horns and posterior median sulcus -has ascending tracts only- carry sensory information from the spinal cord to the brain. * tracts-bundles of myelinated axons in CNS (brain and spinal cord)

2. The lateral white column- includes the white matter on either side of the spinal cord between the anterior and posterior columns- has both ascending (carry sensory information from spinal cord to brain) & descending tracts (convey motor information from brain to the spinal cord).

3. The anterior white column- lies between the anterior gray horns and the anterior median fissure- has both ascending & descending tracts. Spinal Nerves

Nerves are part of peripheral nervous system (PNS).

Functions of the nerves: Bring sensory impulses to the spinal cord. Take motor impulses to the muscles and glands (effectors). Spinal Nerves - Structure

Nerve Muscle

Nerve organization is strikingly similar to muscle organization!

Remember: A muscle is made of fascicles  each fascicle is made of many muscle fibers. Endomysium is connective tissue inside the fascicle. Perimysium is connective tissue around each fascicle. Epimysium is connective tissue that wraps around the entire muscle! Spinal Nerves - Structure

A nerve is the primary structure of the peripheral nervous system (PNS) that encloses the axons of peripheral neurons…made of fascicles  each fascicle is made of a group of nerve fibers (axons).

Endoneurium: is connective tissue around nerve fibers (axons) inside the fascicle. : is connective tissue around each fascicle. : is connective tissue that wraps around all the fascicles to form a nerve! Spinal Nerves - Number

There are 31 pairs of spinal nerves…a total of 62 nerves.

Spinal cord is located in the vertebral canal.

Spinal nerves exit vertebral column through intervertebral foramina.

Intervertebral foramen

Vertebral canal Spinal Nerves - Number

Posterior view Spinal Nerves

Interneuron

Sensory

Sensory fiber

Spinal nerve Motor fiber

All spinal nerves are mixed nerves….contain sensory and motor fibers. Spinal Nerves - Supply N V

C2–C3

C2 C 3 C3

C4 T2 C4 Spinal nerves go to skin, muscles and some C5 T3 T1 T4 of the internal organs. T2 T5 C5 T3 T T 6 4 T7 T5 T8 : areas of the skin that is T2 Dermatomes T6 T9 T T2 T7 10 T11 connected to a specific spinal nerve. T8 T12 T9 C L1 6 T10 L2 L T1 T11 L4 3 C7 Myotomes: specific muscles that are C6 L T12 5 L1 supplied by a specific spinal nerve. S4S L 3 2 S2 C8 C8 T L3 L1 1 1 S5 C7 S1 L5 L4 S2 L2

KEY L5 L Spinal cord regions 3 = Cervical = Thoracic S = Lumbar 1 = Sacral

L4

ANTERIOR POSTERIOR