Anatomy Final Chapter 13 Spinal Cord

Neuronal Pools Five patterns of neural circuits in neuronal pools

1. Divergence 2. Convergence 3. Serial processing 4. Parallel processing 5. Reverberation

Review Questions: 1. Differentiate between divergent and convergent neural circuits. 2. Which kind of neural circuit processes information in a stepwise fashion, one neuron to another? 3. Where does the most complex neural processing occur?

1. Divergence allows one neuron to communicate with many other neurons in a network. Convergence allows a neuron to receive input from many neurons in a network. 2. Serial Processing 3. The brain

Reflexes 5 components of a reflex arc

1. Sensory receptor 2. Sensory neuron 3. Information processing in CNS 4. Motor neuron 5. Effector

Review Questions: 1. When an anesthetic blocks the function of the ventral rami of the lumbar plexus, which areas of the body will be affected? 2. Injury to which of the nerve plexuses would interfere with the ability to breathe? What nerve specifically? 3. An anesthetic blocks the function of the dorsal rami of the cervical spinal nerves. Which areas of the body will be affected?

1. The body wall and lower limbs 2. Cervical plexus, phrenic nerve 3. The skin & muscles of the back of the neck and of the shoulders. Side notes: Dorsal Ramus: deals with sensory or motor information coming from the back Ventral Ramus: deals with sensory or motor information coming from the body wall and limbs Rami communicants: deal with sensory and motor information coming from visceral organs For the Rami communicants remember that white Ramus = preganglionic and gray ramus =postganglionic

Indicate whether the following fibers make up the white rami or gray rami: 1. Preganglionic fibers connecting a spinal nerve with a sympathetic ganglion in the thoracic and lumbar region of the spinal cord 2. Postganglionic fibers connecting a sympathetic ganglion in the thoracic or lumbar region with the spinal nerve 3. Which ramus innervates the skin and skeletal muscles of the back?

1. White Rami b/c white rami is pre ganglionic 2. Gray Rami b/c gray rami is post ganglionic 3. The dorsal ramus contains somatic & visceral motor fibers that innervate the skin & skeletal muscles of the back (The ventral ramus is the larger ramus that innervates everything except the back)

Neuronal Pools

A neuronal pool is a functional group of organized interneurons within the CNS. -Interneurons are organized into functional groups of interconnected neurons. -May be scattered involving neurons in several regions of the brain or localized with neurons restricted to one specific location in the brain or spinal cord. -Each pool has a limited number of input sources and output destinations. -Each pool may contain both excitatory and inhibitory neurons. -The output of the entire neuronal pool may stimulate or depress activity in other parts of the brain or spinal cord, affecting the interpretation of sensory information or the coordination of motor commands.

The Spinal Cord Gross Anatomy

About 18 in. (45 cm) long, 1/2 in (14 mm) wide From Brain only to Vertebrae L1 and L2 5 Regions (cervical, thoracic, lumbar, sacral, coccygeal Has bilateral symmetry Grooves divide spinal cord into left and right Posterior median sulcus: (found on the posterior (dorsal) surface of the spinal cord) Anterior Median Fissure -Deeper groove along the anterior (ventral) surface.

The Spinal Cord Enlargements of the Spinal Cord

Areas of the spinal cord that supply the limbs have more gray matter and are visibly wider. Cervical Enlargement -Supplies shoulder and upper limb Lumbosacral Enlargement -Supplies pelvis and lower limb

Structural Organization Central Nervous System Peripheral Nervous System

CNS -Brain & Spinal Cord -Processing centers PNS -Cranial nerves and spinal nerves -Sensory input and motor response pathways

Neuronal Pools Patterns of neural circuits in neuronal pools Reverberation

Collateral branches of neurons extend back and continue stimulating presynaptic neurons -Forms positive feedback loop; continues until synaptic fatigue or inhibition occurs -Examples: may maintain consciousness, breathing, muscle coordination

Gross Anatomy of the Spinal Cord Features of the Spinal Cord

Consists of (continued): 31 spinal segments - give rise to spinal nerves. Each segment consists of: -Dorsal root -Dorsal root ganglia -Ventral root -Spinal nerve

The Spinal Cord Distal end of the spinal cord

Conus medullaris Tapered, conical end of cord below lumbar enlargement Cauda equina Nerve roots extending below conus medullaris Filum terminale Thin thread of fibrous tissue at end of conus medullaris Attaches to coccygeal ligament

Neuronal Pools Patterns of neural circuits in neuronal pools Convergence

Convergence Several neurons synapse on a single postsynaptic neuron -Through convergence, the same motor neurons can be subject to both conscious and subconscious control. -For example, the movements of your diaphragm and ribs are now being controlled by your brain at the subconscious level. But you can also consciously control the same motor neurons, as when you take a deep breath and hold it. Two neuronal pools are involved, both synapsing on the same motor neurons.

Naming the Spinal Nerves

Designated by vertebral region and number C1 runs above first cervical vertebra C8 below seventh cervical vertebra All others named for vertebrae above Example: T1 is below first thoracic vertebra

Neuronal Pools Patterns of neural circuits in neuronal pools Divergence

Divergence Spreads information from one neuron or neuronal pool to many pools / several neurons. -Especially common in sensory pathways (considerable divergence occurs when sensory neurons bring information into the CNS, because the information is distributed to neuronal pools through the spinal cord and brain) -(Think of it like gossip, how it spreads) -Example: Visual information arriving from the eyes, for example, reaches your consciousness at the same time it is distributed to areas of the brain that control posture and balance at the subconscious level.

Spinal Cord Spinal Meninges are made of 3 layers:

Dura Mater -tough, fibrous outermost layer (Btw. The dura mater and the walls of the vertebral canal lies the epidural space which is a region that contains areolar tissue, blood vessels, and a protective padding of adipose tissue.) Arachnoid mater Middle layer -The cerebrospinal fluid that surrounds the spinal cord is located in the subarachnoid space (under the arachnoid matter), which lies between the epithelium of the arachnoid mater & the pia mater. Pia mater Innermost layer Meningitis -Viral or bacterial infection of meninges -Dangerous because it can disrupt the normal circulation of CSF, damaging or killing neurons and neuroglia in affected areas.

Gross Anatomy of the Spinal Cord Features of the Spinal Nerves

Formed by union of posterior and anterior roots Classified as mixed nerves Sensory nerves (afferent nerves) -Transmit impulses toward the spinal cord Motor nerves (efferent nerves) -Transmit impulses away from the spinal cord

Gray Matter & White Matter of Spinal Cord Functional Organization of Gray Matter Continued..

Gray commissures -Narrow bands of gray matter around central canal -Axons cross here to the other side of spinal cord Sensory or motor nucleus location within gray matter determines which body part it controls

Gray Matter & White Matter of Spinal Cord

Gray matter Cell bodies of neurons, neuroglia, and unmyelinated axons (Gray matter integrates information and initiates commands) White matter Myelinated & unmyelinated axons (White matter carries information from place to place)

View of the spinal cord

Gray matter goes all the way back to the spinal cord. The anterior split is called The anterior median fissure. The tan is the gray area. Dorsal root and ventral root (in yellow) come Together to form central nerve. White matter is your myelinated axons. Gray matter is un-myelinated.

Spinal Cord

Housed within protective membranes (meninges) and the bony vertebral column The spinal cord carries sensory and motor information between the brain and most other parts of body To carry out this function, the spinal cord is the origin of many spinal nerves which allow communication with the peripheral organs -(The spinal cord gives rise to spinal nerves)

Spinal Nerves & Plexuses Cervical Plexus

Includes anterior rami of spinal nerves C1-C5 Innervates scalp behind ear, neck, and diaphragm Major cervical plexus nerve: Phrenic nerve: From C3-C5; controls diaphragm (Won't ask vertebra on any other nerve, just need to know that for this nerve if you damage C3-C5 you die because you won't be able to breathe. DAMAGE FROM C3-C5 IS DEADLY, WON'T BE ABLE TO BREATHE.

Neuronal Pools Patterns of neural circuits in neuronal pools Serial processing

Information moves along a single path, sequentially from one neuron or neuronal pool to the next. -Information is relayed in a stepwise fashion, from one neuron to another or from one neuronal pool to the next -This patters occurs as sensory information is relayed from one part of the brain to another. -Example: Pain signals pass sequentially through two neuronal pools to reach conscious brain.

The Spinal Cord Pia Mater

Innermost Meningeal layer -Is a mesh of collagen and elastic fibers -Firmly attached to underlying neural structures it surrounds -Blood vessels for spinal cord are on surface of the pia mater, within subarachnoid space Paired denticulate ligaments -Anchor pia mater to dura mater -Prevent lateral movement of spinal cord

Spinal Nerves & Plexuses Brachial Plexus (C5-T1)

Innervates the pectoral girdle and upper limbs The ventral rami (Roots) emerging from C5 to T1 form the trunks: Superior trunk Middle trunk Inferior trunk SIDE NOTES: From rami to nerve order: Acronym to help: Really Tired? Drink Coffee Now! (Rami. Trunk, Devisions, Cords, Nerves)

Lumbar Plexus

Major nerve Femoral nerve

Sacral Plexus

Major nerves Sciatic nerve Two branches of the sciatic nerve: Fibular nerve (common fibular nerve) Tibial nerve

Gray Matter & White Matter of Spinal Cord Functional Organization of Gray Matter

Masses of gray matter within the CNS are called nuclei and are organized in the spinal cord into regions called horns. Posterior horns: Somatic and Visceral sensory nuclei (incoming information from receptors) Anterior horns—somatic motor nuclei (outgoing information to effectors) Lateral horns—thoracic & lumbar segments; visceral motor nuclei. Lateral horns are located only in the thoracic & lumbar segments which contain visceral motor nuclei.

The Spinal Cord Arachnoid Matter

Middle meningeal layer Two components: Arachnoid membrane: weblike layer of simple squamous epithelia Arachnoid trabeculae: network of collagen/elastic fibers between arachnoid membrane. Subarachnoid space Space with arachnoid trabeculae, between arachnoid mater and pia mater Filled with cerebrospinal fluid (CSF) that carries dissolved gases, nutrients, wastes Lumbar puncture or spinal tap withdraws CSF from subarachnoid space

Major brachial plexus nerves

Musculocutaneous nerve (lateral cord) Median nerve (lateral and medial cords) Ulnar nerve (medial cord) Axillary nerve (posterior cord) Radial nerve (posterior cord)

Spinal Nerves & Plexuses Nerve Plexuses & The 4 major nerve plexuses

Nerve Plexuses: Complex, interwoven networks of nerve fibers Formed from blended fibers of anterior rami of adjacent spinal nerves Allows multiple spinal nerves to supply the same structures 4 major nerve plexuses: 1. Cervical plexus (Have two know the phrenic nerve, innervates the diaphragm, branches off from C3,C4 and C5 off of those anterior rami) 2. Brachial plexus (Lg. Entanglement of nerves, 5 nerves we need to know, find an "M" if you fine the M you can identify all of them) (Know the 3 cords, then the 5 nerves) 3. Lumbar plexus (know femoral nerve) 4. Sacral plexus (know sciatic nerve)

The Spinal Cord Dura Mater

Outermost meningeal layer -Tough with dense collagen fibers -Continuous with cranial dura mater and fuses with the periosteum of the occipital bone -Distal end tapers to dense cord of collagen fibers; joins filum terminale in coccygeal ligament. Epidural Space -Between vertebrae and dura mater (superficial to dura mater) -Contains loose connective and adipose tissue. Subdural space = potential space deep to dura mater

Reflexes Neural Reflexes

Rapid, automatic involuntary responses to specific stimuli Basic building blocks of neural function A specific reflex produces the same motor response each time

Reflexes Spinal reflexes

Reflexes: -Quick, automatic nerve responses triggered by specific stimuli Spinal reflexes -Controlled by the spinal cord alone without input from the brain -Example: dropping a hot pan. Reflex causes release of the pan before the information reaches the brain and the pain is perceived -Define Spinal Reflex: A spinal reflex is a rapid, automatic response triggered by specific stimuli that is controlled in the spinal cord

Spinal Nerves & Plexuses Peripheral distribution of spinal nerves

Sensory nerves: In addition to motor impulses: -Posterior, anterior, and white rami also carry sensory information. Dermatome: specific bilateral region of skin supplied by a single pair of spinal nerves. Each pair of spinal nerves supplies its own dermatome. Peripheral neuropathies: Regional losses of neural function (sensory and motor function) that affect dermatomes, often from nerve trauma, compression, various illnesses. Shingles—rash/symptoms occur along dermatomes (don't memorize pic)

Functional organization of neurons

Sensory neurons About 10 million; bring information into CNS (incoming) Motor neurons: About 1/2 million; send commands from CNS out to peripheral effectors (outgoing) Interneurons About 20 billion; located within CNS Interpret, plan, and coordinate signals coming in and out

Neuronal Pools Patterns of neural circuits in neuronal pools Parallel processing

Several neurons/neuronal pools process the same information at the same time (simultaneously) -Divergence must take place before parallel processing can occur, as a result several responses can occur simultaneously. -For example, stepping on a sharp object stimulates sensory neurons that distribute the information to several neuronal pools. As a result of parallel processing, you might withdraw your foot, shift your weight, move your arms, feel the pain, and shout "Ouch!" at about the same time. Ex: Walking across campus, see someone, get info on what they look like, what they're wearing, etc. Then you think of memories/if you like them or not so processing diff info at the same time..

What does this image have to do with this lecture?

Showing a spinal tap, put a needle btw. L3 and L4 to remove CSF to check for infections. Spinal cord ends at L2 so you can stick a needle down their and not risk hitting it because it's not there.

Spinal Cord Features of Spinal Meninges

Specialized membranes that provide protection, physical stability, and shock absorption Functions of the spinal meninges: Protecting the spinal cord -Provide physical stability & shock absorption Carry blood supply -(Blood vessels branching within these layers deliver oxygen & nutrients to the spinal cord) Continuous with the cranial (cerebral) meninges At the foramen magnum of the skull, the spinal meninges are continuous with the cranial meninges, which surround the brain. (The cranial meninges have the same three layers.)

Spinal Nerves & Plexuses (Entanglement of Nerves) As the spinal nerves extend into the periphery, they branch & interconnect, forming the peripheral nerves that innervate body tissues and organs.

Spinal nerves Pair of spinal nerves emerges laterally from each spinal cord segment Form by junction of anterior and posterior roots All spinal nerves are mixed nerves (sensory and motor) Peripheral nerves Form from branching and re-sorting of spinal nerves. All are mixed nerves (sensory and motor) Same connective tissue layers as spinal nerves (continuous with each other)

Spinal Nerves & Plexuses Anatomy of Spinal Nerves

Spinal nerves extend to form peripheral nerves, sometimes forming plexuses along the way; these nerves carry sensory and motor information (book) 3 connective tissue layers that surround spinal nerves: Epineurium: Outermost layer ; network of collagen fibers Perineurium: Middle layer; separates the nerve into fascicles (axon bundles) Endoneurium Innermost layer; surrounds individual axons

The Spinal Cord Spinal Nerves and Rami (Branches)

Spinal nerves: Pairs—one from each side at each vertebral level A typical nerve has a white ramus communicans (containing myelinated axons), and a gray ramus communicans (containing unmyelinated fibers that innervate glands and smooth muscle in the body wall or limbs) -"Glands and smooth muscle" tell you it's visceral -A typical spinal nerve also has posterior and anterior rami -Each spinal nerve quickly divides into rami Posterior ramus provides sensory & motor innervation to the skin & muscles of the back. Anterior ramus supplies most of the body wall, skin, limbs -(supplies the ventrolateral body surface, structures in the body wall and the limbs)

Reflexes Events in a spinal reflex arc

Step 1: Stimulus activates a receptor Step 2: With enough stimulation, action potential is generated in sensory neuron. Axon enters spinal cord via posterior root Step 3: Information processing in spinal cord usually occurs at one or more interneurons Step 4: Interneurons stimulate action potentials in motor neuron; its axon leaves via anterior root Step 5: Motor neuron stimulates effector (muscle/gland)

The Spinal Cord Central Canal

The spinal cord has an internal passageway called the central canal. This space is filled with cerebrospinal fluid (CSF), which acts as a shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messengers, and wastes.

The Brachial Plexus (C5-T1)

The trunks form the divisions: Anterior Posterior The divisions form the cords Posterior Lateral Medial The cords form the branches of spinal nerves.

Spinal Nerves

There are 31 pairs of spinal nerves (62 spinal nerves total) 8 cervical nerves 12 thoracic nerves 5 lumbar nerves 5 sacral nerves 1 coccygeal nerve How are the spinal nerves identified? The spinal nerves are identified by its association with the adjacent vertebrae.

Think/Pair/Share

This is a Somatic pathway 1. In red: this is the dorsal root, can see the dorsal root ganglion, it is Afferent because it is sensory only. 2. In Blue: Ventral root, efferent, it is motor

Gray Matter & White Matter of Spinal Cord Structural Organization of white matter

Three columns (regions) (a.k.a. (funiculi) Posterior white columns: Between posterior horns & posterior median sulcus Anterior white columns: Between anterior horns & anterior median fissure (The anterior white columns are interconnected by the anterior white commissure, a region where axons cross from one side of the spinal cord to the other.) -Anterior white commissure: Where axons cross from one side of spinal cord to the other Lateral white columns: On each side of spinal cord, between anterior & posterior columns -The white matter between the anterior & posterior columns on each side makes up the lateral white column.

Gray Matter & White Matter of Spinal Cord Functional Organization of white matter

Tract—bundle of axons in CNS (Side note: what do we call them in the PNS? Nerves) All the axons within a tract relay the same type of information (sensory or motor) in the same direction Ascending tracts— carry sensory information up toward the brain (Afferent) Descending tracts— convey motor commands down to the spinal cord (efferent motor commands, they're going to exit)

The Spinal Cord Spinal roots and ganglia

Two branches form spinal nerves: Anterior root (ventral root)—axons of motor neurons Posterior root (dorsal root )—axons of sensory neurons Spinal nerve roots divide into rootlets before entering or leaving the spinal cord (the roots of all spinal nerves divide in a fanlike fashion which form rootlets). Spinal ganglia (also called dorsal root ganglia) Contain cell bodies of sensory neurons that form the posterior root Located between pedicles of adjacent vertebrae

Gross Anatomy of the Spinal Cord Features of the Spinal Cord Transverse View

White matter Gray matter Central canal - contains cerebral spinal fluid (CSF) Anterior median fissure Posterior median sulcus

Spinal Nerves What can you tell by this picture?

You can tell its a motor pathway because its going through the ventral root (also going out to an effector which lets you know its motor). It's in the lateral gray horn so it's visceral motor, traveling through the rami commuticans which are visceral only Light blue is preganglionic, occurs before the ganglion. (travels through white ramus) Dark blue is postganglionic (travels through gray ramus)