LAB 19: Neurons, the Spinal Cord, and Spinal Nerves

Central Nervous System (CNS) consists of

the brain and spinal cord

What problems would a person have if all of her ventral roots were cut? If dorsal roots were cut?

- Cut ventral roots = effectors not being able to receive motor commands - Cut dorsal roots = spinal cords not receiving sensory information

Gross Anatomy of the Spinal Cord

- Extends superiorly from the Foramen Magnum to L1 or L2, and occupies the vertebral foramina of the vertebrae. - The inferior tip of the spinal cord is called CONUS MEDULLARIS. Then spinal nerves exits the spine from the atlas, C1 to the coccyx. - Beneath the conus medullaris are spinal nerves in form a horse tail called CAUDA EQUINA. - The FILUM TERMINALE, is an extension of the pia mater of the spinal cord that attaches the conus medullaris to the Coccyx - LUMBAR, SACRAL and COCCYGEAL Spinal nerves attach to the inferior portion of the spinal cord - Cervical and Lumbosacral Enlargements (plexuses) contain the cell bodies of the many spinal nerves to innervate the upper and lower limbs respectively, both contains sensory and motor neurons. - POSTERIOR MEDIAN SULCUS = Back of the spine - ANTERIOR MEDIAN FISSURE = front - Ascending and descending white matter tracts carry information to/away from brain

Key terms to identify in a MOTOR neuron -Define Synapse

- SOMA = cell body, contains nucleus -DENDRITE = receive information -TELODENDRIA/ SYNAPTIC KNOB of a motor neuron = branched extensions of other axons from other neurons. -AXON TERMINAL = ends of the telodendria that will synapse with the dendrite and soma of another neuron and release neurotransmitters. - AXON HILLOCK- Beginning of the axon; initiation of Action potential. - AXON is covered with AXOLEMMA, Plasma membrane which contains NEUROLEMMOCYTES (Schwann cells) which forms the MYELIN SHEATHS that protect the axon, electrically insulate the axon and increase the speed of an action potential. - Gaps btw the neurolemmocytes are called NEUROFIBRIL NODES (Nodes of Ranvier) for action potential propagation. - The myelinated axons are wrapped in a connective tissue called ENDONEURIUM. -SYNAPSE = the junction btw 2 neurons or btw a neuron and an effector cells.

Cross-sectional anatomy of the spinal cord

- Spinal cord is like a long tube with a CENTRAL CANAL that is filled with CSF, running down the middle. -Contains 2 nervous tissue; White And Gray mater. Gray matter (unmyelinated axons, glial cells and neuron bodies and dendrites) is located in core, white matter outside (myelinated axons and glial cells) - The gray mater has a Butterfly-shape appearance that contains; ANTERIOR HORN (contains somatic motor neuron bodies) and POSTERIOR HORN (contains interneuron bodies) -Thoracic and superior lumbar region of the cord has a LATERAL HORN (contains Visceral motor neuron) - The portion of Grey mater that connects the 2 wings is the GRAY COMMISSURE - The white mater surrounding the gray mater has ANTERIOR FUNICULI (carry signals from the brain to cord, Descending, Motor neuron) POSTERIOR FUNICULI (carry signals to the brain, Ascending, Sensory neuron) LATERAL FUNICULI (Both ascending and descending axons) - Ventral (anterior) median fissure = separates the L & R anterior funiculi -Dorsal (posterior) median sulcus = separates the L & R posterior funiculi EXTRA INFO: - Motor neurons exit the front of the spinal cord via nerves called VENTRAL ROOTS. - Sensory neuron bodies are located in the DORSAL ROOT GANGLIA, and their axons travel in the back of the cord via nerves called DORSAL ROOTS *A ganglion is a structure that contains neuron bodies and lies outside the CNS - The dorsal and ventral root come together to form the 31 spinal nerves on both sides of the cord that carries both sensory and motor neuron ANTERIOR/VENTRAL = MOTOR POSTERIOR/DORSAL = SENSORY

Describe the function of a SOMATIC MOTOR neuron and its main structures.

-The GENERAL FUNCTION of a neuron is to respond to a stimulus by generating an electrical impulse that will signal another cell - GENERAL STRUCTURES are; 1. One or more DENDRITES; to receive information/stimulation from other neurons. 2. Cell body called SOMA that contains a Nucleus and Nissl body, similar to Rough E.R for protein synthesis. 3. An AXON, to send electrical impulse to another cell or cells of a SKELETAL muscle. SOMATIC MOTOR neuron are MULTIPOLAR neurons, which means it has multiple DENDRITES, and a single AXON extending from its SOMA SENSORY neuron are UNIPOLAR, has one process, that acts as both a dendrite and axon, attached to it -GLIAL cells are present

3 functions of the spinal cord

1. Pathway for SENSORY information traveling UPWARD from the periphery to the brain. 2. Pathway for MOTOR information traveling DOWNWARD from the brain to the periphery 3. It processes information and can acts as a major reflex center. -The 31 pairs of spinal nerves carry information to and from the spinal cord; just as the 12 cranial nerves is to and from the brain

Briefly describe the cell of the nervous system, Neurons; 3 types

Neurons send signal to other neurons and to effectors. 1. SENSORY neurons (AFFERENT): Send signals from sensory receptors to the CNS. 2. INTERNEURONS (CONTROL CENTER): send received signals to other neurons within the CNS. 3. MOTOR neurons (EFFERENT): send signals from the CNS to effectors, which are glands and muscle cells (smooth, cardiac, and skeletal) -VISCERAL MOTOR neuron: send signals to glands, cardiac and smooth muscle cells -SOMATIC MOTOR neuron: send signals to Skeletal muscle cells.

Describe spinal meninges

Spinal meninges are similar to cranial meninges. They have 3 meningeal layers 1. PIA Mater = *SUBARACHNOID SPACE btw the arachnoid and pia mater, that contains CSF Fluid 2. ARACHNOID Mater = 3. DURA Mater = ONLY one set of dura mater (compared to the cranial dura mater that has 2, meningeal and periosteal) *EPIDURAL SPACE btw the spinal dura mater and surrounding vertebrae, that contains ADIPOSE tissue and blood vessels (compared to Cranial meninges that doesn't have Epidural space)

Define Dermatome

an area of the skin supplied by a single pair of spinal nerve, done with the use of a dermatome map. Example; medial surface of the left arm is innervated by left C8 spinal nerve SUMMARY OF THE 31 MIXED SPINAL NERES 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccyx (Filum Terminale) (NORMAL VERTEBRAE COUNT; C7, T12, L5, S1, Co1)