ANATOMY Exam Two

Neurons in the CNS

Located in the Gray Matter

Axons in the CNS

Located in the White Matter

Neurons in PNS

Located in the Ganglia

AXONS in the PNS

Travel together to form Nerves

Bipolar Neurons

  are special sensory neurons only found in special sense organs: retina of the eye, olfactory epithelium in the nose, inner ear, tongue tastebuds (modified).

Psuedounipolar neurons

general sensory neurons ONLY found in PNS sensory ganglia.

Motor Neurons

located in the CNS brain and spinal cord. In the PNS, they are located in autonomic motor ganglia.

Sensory Ganglia

ontain NCBs of pseudounipolar neurons

Ganglia

clusters of neuron NCBS

Dorsal Root Ganglia

associated with spinal nerves

(Sensory Ganglia)

Cranial Nerve Sensory Ganglia

along cranial nerve

(Sensory Ganglia)

 

Autonomic motor ganglia

contain NCBs of motor (multipolar) neurons

Sympathetic and Parasympathetic systems are a part of this

Sympathetic chain ganglia:

outside the vertebral column

Prevertebral (preaortic) ganglia (sympathetic)

neurons in abdomen

Cranial nerve motor ganglia (Parasympathetic)

along cranial nerves (Parasympathetic)

Intramural ganglia (Parasympathetic)

microscopic, in the walls of organs

Peripheral Nerves

A nerve to a particular tissue is like a tube that carries many axons. These axons may be the axons of motor neurons or axons of pseudounipolar sensory neurons.

Spinal nerves (31 pairs):

 innervate the limbs and body wall from the neck on down. (peripheral Nerves)

Cranial nerves (12 pairs):

innervate head & neck structures as well as thoracic and abdominal organs. (peripheral nerves)

Spinal Cord

Outer white matter columns (tracts of axons)

Inner gray matter

·      Dorsal (posterior) horn

·      Ventral (anterior) horn

·      Lateral horn: only found at spinal cord levels associated with the autonomic NS

Ventral Root

carries motor neuron axonsfrom the spinal cord to the muscles.

Joins with dorsal root to make spinal nerve

Dorsal Roots

carries central processes (axons) of pseudounipolar neurons. Each dorsal root extends to a dorsal root ganglion where the NCBs are located.

Joins with Ventral root to for, spinal nerve

Spinal Nerves

·      31 pairs of spinal nerves, each pair arise from a spinal cord segment (area of SC which gives rise to a pair of spinal nerves)

·      There are 8 cervical spinal nerves (C1-C8), 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal

·      The SC is surrounded by and protected by the vertebral column. The dorsal and ventral roots join to form the spinal nerve just before exiting the vertebral column. The spinal nerve exits the vertebral column through the intervertebral foramina, a space located between the stacked vertebra. 

·      The spinal cord is shorter than the vertebral column and ends approximately at the level of lumbar vertebra 3 (L3). Since the SC is shorter than the vertebral column, the lower spinal nerve roots must extend farther inferiorly in order to exit through the correct intervertebral foramina.  This creates an inferior “tail” of nerve roots called the Cauda equina (horse’s tail).

L3

Where must Lunbar puncture or spinal taps be performed so the needle does not hit the spinal nerve

Dorsal ramus:

gives rise to nerves that innervate the back proper

Ventral ramus

gives rise to nerves that innervate the anterior body and limbs

Nerve plexus

Ventral rami of spinal nerves give rise to nerve roots that branch and join forming collections of nerves

Cervical plexus (formed by spinal nerves C1-C5):

·      gives rise to nerves that innervate the anterior neck region. Spinal nerves C3-C5 carry axons that form the phrenic nerve which innervates the diaphragmand is crucial for respiration.

Brachial plexus (C5-T1):

gives rise to nerves that innervate the upper limb

Lumbar plexus (T12-L4)

gives rise to nerves that innervate the lower limb

Sacral plexus (L4-S4)

gives rise to nerves that innervate the pelvic and gluteal region

Somatic tissues

skin, skeletal muscle (also tendons, bone, ligaments)

• Skeletal muscle receives motor innervation and sensory innervation (proprioception is our muscle position sense)

• Skin receives sensory innervation (pain, thermal, touch, pressure, stretch)

Visceral tissues

·      Cardiac muscle, smooth muscle and glands receive motor innervation.

• Visceral motor is handled by the autonomic nervous system (ANS)

• Visceral tissues receive sensory innervation too but it is more complex and not handled by the ANS

 

Spinal nerves innervate the outer body:

·      The outer body is the limbs, back and anterior body wall. This includes all somatic components (skeletal muscle, skin) as well as the visceral tissues: glands of the skin, smooth muscle of the blood vessels and smooth muscle arrector pili. Arrector pili attach to hair follicles and when they contract, it makes the hair erect (goosebumps)

The 3 components that make the Spinal Nerve

• Somatic motor axons to skeletal muscle.

• Somatic sensory axons from skin and muscle.

• Autonomic motor axons to viscera in the body wall (blood vessels, sweat glands, arrector pili muscles)

Somatic Motor pathway:

Motor neurons are located in the SC ventral horn. They extend their axons through the ventral root and then through spinal nerves and their branches to synapse on skeletal muscle Make up this pathway

Somatic Sensory pathway:

Pseudounipolar neurons are located in the dorsal root ganglia. Their peripheral process originates as a receptor ending in the skin and muscle. Sensory impulses are conveyed by the peripheral process which passes through the spinal nerve to the neuron NCB in the dorsal root ganglia. Impulses are then conveyed through the central process to the spinal cord. Make up that pathway

Spinal nerve mapping:

Spinal nerves have specific distribution patterns. For example: specific nerve branches from the brachial plexus will provide motor innervation to specific skeletal muscles of the upper extremity (limb) and sensory innervation to the skin covering that area. If the spinal nerves to the upper limb are damaged, the patient will lose motor function of muscles in the upper limb (weakness or paralysis) and experience loss of sensation (parasthesia) in the area of the upper limb that the spinal nerve supplies.

Shingles

• Varicella zoster virus causes Chicken pox in children. After infection, the virus remains latent (inactive) in sensory neurons in the dorsal root ganglia or cranial nerve ganglia

• Reactivation can occur in adults. The virus in the sensory ganglia “wakes-up” and multiplies and travels down sensory axons to the skin causing skin infection (blistering) in areas supplied by the sensory neurons.

Autonomic Nervous System

All visceral tissue (smooth muscle, cardiac muscle and glands) receives motor innervation from a part of the PNS called the

Made up of two parts:

• Sympathetic (thoraco-lumbar): sympathetic stimulation increases heart rate, respiration and directs blood flow to skeletal muscle

• Parasympathetic (cranio-sacral): parasympathetic stimulation decreases heart rate, increases digestive function and controls sexual arousal

• Internal organs are innervated by both sympathetic and parasympathetic nerves.

• The outer body viscera receive only sympathetic innervation

motor pathways to viscera are 2 neuron “hook-ups”

• A preganglionic motor neuron (NCB) is located in the CNS.

• The axon of this neuron, or preganglionic axon (fiber), synapses on a ganglionic neuron located in a motor ganglion the PNS.

• The axon of the ganglionic neuron (postganglionic axon or nerve fiber), then synapses on glands, smooth muscle or cardiac muscle.

Sympathetic Pathways

• For innervation of all visceral tissues, the sympathetic preganglionic neuron is always located in the lateral horn in SC levels T1 to L3. The preganglionic axon then travels out through the ventral horn and ventral root. It then travels through a short nerve segment called a ramus communicans to reach the sympathetic chain.

 

For viscera of outer body (skin glands, vessel smooth muscle, arrector pili:

·      The preganglionic axon synapses on a ganglionic neuron located in the sympathetic chain ganglia.

• The postganglionic axon must utilize the spinal nerve as a route to get to the outer body. The postganglionic axon goes back through a ramus communicans to join the spinal nerve and travels though branches of the spinal nerve to innervate outer body viscera.

• So the third component to a spinal nerve is sympathetic postganglionic axons carrying motor innervation to blood vessel smooth muscle, skin glands and arrector pili smooth muscle.

• If an entire spinal nerve is cut, there will be loss of motor innervation to skeletal muscle, loss of sensory to skin and skeletal muscle AND loss of sympathetic motor innervation to viscera in the area supplied by that spinal nerve (skin flushing or coldness, sweat secretion changes).

 

Internal visceral organs:

·      Smooth muscle, cardiac muscle and glands are located in internal organs. These visceral tissues receive BOTH sympathetic and parasympathetic autonomic motor innervation.

·      Spinal nerves DO NOT innervate internal organs. Special visceral nerves carry the motor axons to the visceral tissues.

 

Sympathetic innervation to visceral organs:

·      The sympathetic preganglionic neuron is located in the lateral horn of the SC levels T1-L3.

·      The preganglionic axon travels out the ventral horn and ventral root. It then travels through the ramus communicans to the sympathetic chain ganglia.

·      The preganglionic axons synapses on the ganglionic neuron in the sympathetic chain ganglia (for internal organs of the upper body) OR it passes through the sympathetic chain and travels to the prevertebral ganglia where it synapses on the ganglionic neuron (for lower body internal organs).

·      The postganglionic axon then travels through visceral nerves to the organs.

 

Parasympathetic Innervation of visceral organs

·      The nerves that provide parasympathetic innervation to the deep visceral organs are the Cranial nerves (12 pairs) as well as the pelvic splanchnic nerves.

·      The cranial nerves innervate visceral organs of the head down to the lower abdomen.

·      The pelvic splanchnic nerves innervate pelvic visceral organs.

 

For visceral organs of the head down to the lower abdomen:

·      The parasympathetic preganglionic neuron is located in the brain in Cranial nerve nuclei. The preganglionic axons travel through cranial nerve branches to synapse on ganglionic neurons located in parasympathetic motor ganglia.

·      The ganglionic neurons are located in cranial nerve motor ganglia for visceral organs of the head and in intramural ganglia (tiny ganglia) located in the walls of visceral organs of the thorax and abdomen.

·      Postganglionic axons are short and travel to the visceral tissues.

 

For visceral organs of the pelvis (urinary and reproductive organs)

• The preganglionic neurons are located in the lateral horn of the sacral spinal cord. Preganglionic axons travel through the ventral root and exit the SC and form the Pelvic splanchnic nerves. Preganglionic axons travel through branches of the pelvic splanchnic nerves to the visceral organs where they synapse in intramural ganglia. Postganglionic axons are very short and in the walls of the organs.

Anatomical position

toes forward, palms facing forward

Axial skeleton

Skull and associated bones:

• The skull bones develop by intramembranous bone formation.  Multiple bones develop as “islands or plates” of bone which later fuse.  This allows for growth of the brain.  Growth and fusion of skull bones continues into childhood. 

• At birth, the skull bones are separated by dense CT referred to as the fontanels

• Major skull bones: frontal, parietal (2), occipital, temporal (2), sphenoid, ethmoid, mandible, maxilla (2), palatine (2), zygomatic (2)

• Hyoid bone: floating bone in neck located superior to the larynx, provides attachment for neck muscles

Fontanels

At birth, the skull bones are separated by dense CT referred to as the

Hyoid bone

floating bone in neck located superior to the larynx, provides attachment for neck muscles

 

Vertebral column

·      Seven cervical vertebrae, 12 thoracic, 5 lumbar, 5 fused sacral, 3-5 coccygeal bones (coccyx) may be fused

·      Intervertebral discs: cartilage and CT cushions between stacked vertebrae

·      Basic structure of vertebrae:

            Centrum (body)

            Vertebral arch

            Vertebral canal: location of the SC

            Spinous process

            Transverse process

            Articular facets

            Intervertebral foramen: spinal nerves exit through

Basic Skeletal Concepts

·      From superior to inferior, the spinal cord decreases in diameter therefore the vertebral canals also decrease in diameter.

·      The weight load put on the vertebral column increases from superior to inferior therefore the vertebral centra increase in size with the sacrum fused for greatest stability.

·      Normal spinal curvatures allow for proper weight distribution and bring the weight of the body and limbs into alignment with the central axis of the body

• Cervical, thoracic, lumbar, sacral

Kyphosis

abnormally rounded upper back (“hump” condition)

Lordosis

exaggerated lumbar curvature

Scoliosis (“twisted condition”):

lateral, sideways or “s” shaped curvature

Cervical vertebra (7)

The only vertebrae with transverse foramen, the vertebral artery passes through this foramen

Atlas (Greek God who supported the heavens

C1

• Articulates with the occipital bone of the skull

• No true spinous process, has a small tubercle instead that allows for nodding of the head

  • No intervertebral disc between C1 and C2

Axis (center axle about which things pivot)

• An anterior projection called the dens or odontoid process projects up and rotates with an articular facet on the inside of the atlas vertebral canal allowing for circular rotation of the head.

• A ligament called the transverse ligament of the atlas hold the dens in place and prevents it from moving posteriorly into the spinal cord.

• During development, the vertebrae form “in pieces” with complete fusion of the pieces occurring through childhood and into early adulthood. Incomplete fusion in childhood makes the vertebrae less stable and prone to separation if trauma occurs.

• In infants, the neck muscles and ligaments are not well developed and the head is proportionally larger and heavier. This makes the C1-C2 joint less stable and susceptible to injury.

  • Transverse ligament damage and dens fractures occur in children and adults and can cause SC or brain injury.

 

Thoracic vertebrae (12):

Articulate with the ribs, long spinous process

Lumbar vertebrae (5)

Large centrum, thick spinous process

Sacral vertebrae (5)

Fusion of the 5 vertebrae begins after puberty

Coccyx

3 to 5 small vertebrae begin fusing after about 25 years

Thoracic cage

 ribs and sternum

12 pairs of ribs:

• All ribs articulate with the thoracic vertebrae

• 1 to 7: true ribs attach by individual costal cartilages to sternum

• 8 to 10: false ribs costal cartilages fuse before attaching to the sternum (they share a costal margin)

• 11and 12: floating ribs have no connection to the sternum

Sternum

·      Articulates with the clavicle and rib costal cartilages

·      Manubrium, body, xiphoid processForms the protective ribcage

Pectoral girdle

• Consists of the scapula and clavicle

• Positions shoulder and moves upper extremity, allows for great mobility

• Clavicle: articulates with the sternum and scapula

• Scapula: glenoid fossa articulates with humerus

Upper extremity

• Humerus (arm): proximal head articulates with the scapula. Distal condyles articulate with the radius and ulna

• Radius and Ulna (forearm): articulate with each other and the humerus and carpal bones

o   Ulna: olecranon process (elbow)

o   Radius: flat circular head

• Carpal bones (wrist): 8 bones in 2 rows of 4

• Metacarpals: 5 bones of the hand

• Phalanges (digits): finger bones (thumb 2, other digits 3)

Hip (pelvic girdle):

3 fused bones: ilium, ischium, pubic bone

• Acetabulum: articulates with the femur

• Obturator foramen: large opening, blood vessels and nerves pass through

Bony Pelvis

• The bony pelvis forms a circular framework which has a superior opening or inlet and an inferior opening or outlet. 

• The bones of the pelvis include the 3 hip bones as well as the posterior sacrum and coccyx. 

• The ilium articulates with the sacrum and flares out laterally in a curving fashion to form the lateral aspect of the bony pelvis. 

• The pubic bone extends anteriorly from the ilium and joins with the opposite pubic bone to form a midline joint called the pubic symphysis. 

• From a superior viewpoint looking down into the pelvis, the borders of the pelvic inlet are the posterior sacrum, the upper curved border of the ilium and the superior border of the pubic bones and pubic symphysis. 

• From an inferior viewpoint looking up into the pelvis, the borders of the pelvic outlet are the posterior coccyx and sacrum and the inferior borders of the ischium and pubic bones.

Female adaptations for childbearing:

• A wider more circular pelvic inlet

• Sacrum is shorter and wider with a flatter curvature

• Coccyx tilts posteriorly

• Larger pubic bone

• The inferior angle between the opposite pubic bones is farther apart

• The ilium projects farther laterally

 

Lower extremity (lower limb):

• Femur (thigh): proximal head articulates with the acetabulum, 2 distal condyles articulate with the tibia and patella

• Patella (kneecap)

• Tibia and fibula (leg): articulate with each other and the talus

o   Tibia: medial larger bone, also articulates with the femur

o   Fibula: slender lateral bone

• Tarsal bones (ankle): 7 bones

  • The talus and calcaneus bones bear the entire weight of the body

• Metatarsals: 5 form the arch of the foot

• Phalanges (digits,toes): big toe 2, other digits 3

Synarthroses

immovable (sutures of skull) (joint movement)

Amphiarthroses

slightly movable (pubic symphysis, vertebral) (joint movement)

Diarthroses

freely movable (synovial joint) (joint movement)

Synovial joints

·      Articular cartilage on the ends of the bones: hyaline cartilage

·      Joint capsule: outer dense CT, inner synovial membrane

·      Synovial membrane: inner surface consists of synovial cells that secrete a viscous fluid.

·      Synovial fluid: combination of synovial cell secretion, capillary ultrafiltrate and WBCs

·      In some joints, the synovial lined sac is called a bursa. Inflammation of the bursa: bursitis

Osteoarthritis

 

degenerative disorder of the articular cartilage due to excessive wear and tear. Occurs in isolated joints exposed to excessive wear. Inflammation is secondary. Cartilage erosion followed by bone degeneration

Rheumatoid arthritis

systemic chronic inflammatory disorder. Occurs in multiple joints. Chronic relapsing inflammation of joints. Inflammatory cells infiltrate the joint and release factors that destroy the articular cartilage and adjacent bone. Ankylosis (fusion) of joints may occur.

Gout (hyperuricaemia)

precipitation of urate crystals in joint causes acute inflammatory reaction. Usually the cause is unknown but can result from chronic renal disease (kidney can’t excrete urate).

Abduction

to take away from the midline

Adduction

to add (move closer) to the midline

Flexion:

“to bend” refers to one bone moving closer to an adjacent boneFlexion

Extension

“to make larger” refers to one bone moving farther away from another bone.`

Pronation

prone means to lie flat. Pronation refers to twisting at the elbow and wrist so palms faces downward.

Supination

supine means facing upward, refers to twisting of the elbow or wrist so the palm faces upward.

Plantarflexion of the ankle

ankle movement results in toes moving towards heel

Dorsiflexion of ankle

ankle movement results in toes moving towards anterior leg