anatomy 403 neuro

What are the components of the CNS?

Brain (forebrain, brain stem, cerebellum) and spinal cord (cervical, thoracic, lumbar, sacral, coccygeal)

What are the components of the PNS?

Cranial nerves (know origins) and Spinal nerves

Define afferent signals/information

Neuronal projections to a neuron, group of neurons, or central NS = AFFERENT ARRIVES

Define efferent signals/information

Neuronal projections from a neuron, group of neurons, or central NS = EFFERENT EXITS

What is the difference between the autonomic and somatic nervous systems?

Somatic is conscious (with sensory and motor). Visceral is unconscious (with sensory and motor) where the motor aspect is autonomic (does daily work of life, heartbeat, respiration, digestion)

What are 3 functions of the nervous system?

Sensory, Integrative (interneurons within the brain and spinal cord play a role in analyzing and integrating sensory info), motor function 

nucleus

a group of neurons within the CNS with similar function, connectivity, adn neurotransmitters

tract

a bundle of axons traveling together within the CNS

synapse

a point of connection/communication between neurons

ganglia

a group of neurons outside of the CNS with similar function connectivity and neurotransmitters

nerve

a bundle of axons plus Associated connective tissue and blood vessels located outside the brain and spinal cord

somatic NS

afferent and efferent systems that regulate motor innervation of skeletal muscle and relay sensory information from the external environment

autonomic motor NS

efferent systems that regulate motor innervation of smooth muscle and glands

Visceral sensory system

afferent sensory information from the internal environment (hollow organs) 

gray matter

contains neurons and their proximal dendrites

white matter

contains myelinated axons

What are the important characteristics of neurons?

Highly specialized and excitable. Have all the organelles as others cells with some specializations

What are the 3 types of neurons in vertebrates?

Multipolar = 1 axon and many dendrites. Bipolar = 1 axon and 1 main dendrite (rods and cones in retina). Psuedo-unipolar = 1 process exits the soma and splits into a central and peripheral process (primary sensory neurons of the dorsal root ganglia).

list the components of a synapse.

Electro-chemical, site of communication between two neurons, presynaptic neuron = neuron carrying an impulse toward the synapse (axon), post synaptic = neuron carrying an impulse away from the synapse (dendrite). A synapse between a neuron and a muscle fiber = a neuromuscular junction. Presynaptic have vesicles. 

Ependymal

CNS.

• Line ventricles of the brain

• Have cilia for moving CSF

• + Capillaries form choroid plexus 

• Form brain = cerebrospinal fluid barrier

Oligodendrocytes

CNS

• Myelinating glia of the CNS

• One oligodendrocyte may myelinate many axons

• Myelin is mainly lipid and contributes to the appearance of CNS white matter

Astrocytes

CNS

• Induce formation of tight junctions

• Blood brain barrier

• Contact with capillaries, neurons, and the pia mater

Microglia

CNS

• They originate in bone marrow and migrate to CNS 

• Function as phagocytes and remove cellular debris, microbes, and damaged nervous tissue 

Neuroglia

constitute approximately half the volume of the CNS, smaller than neurons, do not generate or propagate impulses, retain the ability to divide in the mature nervous system. 

Satellite

PNS. Act like astrocytes. Surround individual neurons for protection and support

Schwann

PNS. Only myelinate 1 axon

why is the BBB important?

protects brain cells from harmful substances and pathogens. Consists of tight junctions between the endothelial cells of brain capillaries and the foot processes of astrocytes. Presents a challenge to drug design. 

Dura

• most superficial layer. Super tough

• Two layers

  • Periosteal (same as layer that covers bone)

  • Meningeal

• Specializations

  • Falx cerebri

    • Dural sinuses

  • Falx cerebelli

  • Tentorium cerebelli

    • Perpendicular to other 2 layers

    • Dural sinuses

Arachnoid

• encloses subarachnoid space 

• Filled with cerebrospinal fluid

• Blood vessels

• Allows brain to float

• Arachnoid granulations

Pia

• Covers every surface of brain and spinal cord

What structure creates cerebrospinal fluid and where is it found?

Choroid plexus

What subdivisions of the lateral ventricle are associated with the frontal lobe?

anterior

What subdivisions of the lateral ventricle are associated with the temporal lobe?

inferior horn

What subdivisions of the lateral ventricle are associated with the parietal lobe?

body

What subdivisions of the lateral ventricle are associated with the occipital lobe?

posterior horn

Which ventricle is found within the diencephalon?

third

Which ventricle is found within the brain stem?

fourth

What is its path of cerebrospinal fluid through and out of the ventricles (from creation to absorption)?

Secreted by the CHOROID PLEXUS into all ventricles → flows out of the ventricles into the SUBARACHNOID SPACE through 3 foramina. Two lateral apertures in each lateral recess, and one medial aperture. Circulates in the subarachnoid space around the brain and spinal cord. Flows into the venous blood stream through the ARACHNOID GRANULATIONS (one way valves) into the DURAL SINUSES

What two arteries are the main contributions to the cerebral vascular circle?

Internal carotid and vertebral 

What larger artery is the source of these arteries?

Cerebral Vascular Circle

What are the 3 main branches of the cerebral vascular circle and what areas of the brain do they supply? 

??

Internal carotid

1. Anterior communicating

   1. Medial aspects of the frontal and parietal lobes

2. Middle cerebral artery

   1. Frontal, partial, temporal. Supplies insula

3. Posterior communicating

Vertebral

• Two vertebral arteries fuse to form basilar a. Branch of basilar is the posterior cerebral a. 

  • This artery supplies medial and lateral aspect of occipital lobe 

What happens if the anterior neuropore fails to close?

Anencephaly

What happens if the caurdal neuropore fails to close?

Spina Bifida

What forms the ventricular system?

The ventricles develop from the lumen within the neural tube

Each ventricle associated with a region of the CNS

Lateral: cerebral hemispheres

Third: diencephalon

Fourth: brain stem

Where is the neural crest formed and what are the different cell types does it become?

Separates from the neural tube, cells are proliferative, migratory nerve progenitors that form the peripheral nervous system. Become: dorsal root ganglia neurons, autonomic ganglia neurons, pia mater,  schwann cells, satellite cells, melanocytes

What are the 4 essential functions of the spinal cord?

Relays sensory info from periphery to brain, somatic and visceral. Contains motor neurons both somatic and visceral. Direct (local) connections between motor and sensory information: reflexes. Relays motor information from brain to muscles, somatic and visceral.

Describe the divisions/areas of the gray matter and white matter in the spinal cord.

Outer layer is white matter (axons and surrounding myelin) divided into columns calls funiculi. Inner layer is gray matter: neuronal cell bodies, proximal dendrites, and astrocytes. 

Do all 3 meningeal layers cover the spinal cord?

How is the dura different in the vertebral canal compared to that of the cranium? The dura has epidural adipose tissue and does not form the periosteum of vertebral bones because they are bendy. Different to the two layers in the brain. 

All three layers are continuous along the spiral cord. Fuse with the epineurium. 

Pia is immediately adherent to surface of spinal cord. 

Dural Sac

where CSF is held in spinal cord

Cauda equina

bundle of spinal nerves traveling to their appropriate exit points. 

Filum Terminale, Internus

thread-like extension of the pia mater from the conus medullaris of the spinal cord. Anchors spinal cord to dural sac.

Filum Terminale, Externus

thread-like extension of the dura mater below the end of the dural sac S2. it attaches to the coccyx. Also known as the coccygeal ligament. Anchors dural sac to bottom of column

How many regions are there in the spinal cord and what are their names?

How many enlargements in the spinal cord

2: cervical and lumbar

Name the nuclear groups (columns) in the dorsal horn of the spinal cord and name their functions.

Substantia Gelatinosa, nucleus proprius, dorsal nucleus. SENSORY relays. 

Do all of the nuclear groups in the spinal cord gray matter continue the entire length of the cord? Be able to know which do and which do not.

Ventral horn medial and the substantia gelatinosa/nucleus proprius are continuous. The others are not. 

Describe the somatotopic map of the spinal cord ventral horn.

1. Medial neurons innervate most proximal muscles. Most lateral innervate the most distal muscles. 2. Motor neurons that innervate extensor muscles: ventral,  flexor muscles: dorsal

What types of fibers travel in the spinal cord white matter?

Dorsal, lateral, and ventral funiculi (columns).  

Describe the blood supply of the spinal cord.

Vertebral arteries 

• 1 ventral anterior spinal artery

• 2 dorsal 

  • Branches of the vertebral a

  • Supplemented by branches from the aorta!

Spinal arteries branch to form a corona around the spinal cord and also send branches to the vertebrae. It is possible to have a stroke in the spinal cord. 

Define a spinal nerve

Spinal nerves pass out of the vertebral column via the intervertebral foramen. Exit above named cervical body, so there is one more nerve than spinal body. 

A spinal segment is the functional unit of the spinal cord. Spinal nerves divide into dorsal and ventral primary rami. 

How many pairs of spinal nerves are there?

31

What is a plexus?

 many spinal nerves come together to form plexuses. 

What is a dermatome?

 the area of the body’s surface innervated by one pair of spinal nerves. Dermatomes overlap. 

What is a receptive/cutaneous field?

area of skin innervated by 1 dorsal root ganglia neuron. Subset of each dermatome. 

What is a motor unit?

total number of skeletal muscle fibers innervated by one alpha motor neuron. Can be big or small. Small motor units are for fine control.

What are the terminal branches of Cervical Plexes? 

cervical spinal nerves 1-5, motor branches: phrenic nerve, sensory: lesser occipital, great auricular, transverse cervical, supraclavicular

What are the terminal branches of Brachial plexes

terminal branches are mixed, they contain motor and sensory fibers,  C5-T1

• axillary (deltoid), 

• musculocutaneous (elbow fibers), 

• median (wrist/finger flexors), 

• radial (elbow, wrist, finger extensors), 

• ulnar (wrist/finger flexors). 

• Areas of plexus: Robert roots Taylor trunks Drinks divisions Cold cords Beer *branches (the named nerves in periphery).

What are the terminal branches of Lumbar plexes

terminal branches are mixed. L1-L5

• Iliohypogastric

  • Skin and muscle of anterior body wall

• Illioinguinal

  • Skin and muscle of anterior body wall

• Genitofemoral

  • Skin of the scrotum and labia majora, cremaster muscle

• Lateral cutaneous

  • Skin of lateral thigh

• Femoral

  • Skin of anterior thing, knee extensors

• Obturator

  • Skin of medial thigh, adductors (medial compartment)

What are the terminal branches of Sacral plexes

terminal branches are mixed L4-S5

• Superior gluteal n

  • Gluteus medius and minimus

• Inferior gluteal n

  • Gluteus maximus

• Pudendal n

  • Innervates perineum 

• Sciatic (2 components)

  • Muscles of posterior thigh

  • Tibial n

    • Posterior leg

  • Common fibular 

    • Anterior and lateral leg

What types of cells and tissues do you find in a peripheral nerve and what are the connective tissue elements that surround a nerve, a fascicle and an axon?

Epineurium surrounds the nerve, bundle of axons within the nerve are surround by perineurium, and each individual nerve fiber is surrounded by endoneurium. Fibroblasts secrete collagen and components of perineurium. Shwann cells. Macrophages. 

Tendon/stretch/patellar reflex

monosynaptic reflex because there is no interneuron between the central projection of the sensory neuron and the responding motor neuron. Because there is direct link between dorsal root ganglion and motor neuron.

Flexor/pain reflex

polysynaptic. Contraction of flexor muscles in response to pain and inhibition of antagonist muscles (extensors)

Crossed extensor reflex

pain on a limb that bears weight. Excited by the afferents of the flexor reflex. Interneurons send axons to the contralateral ventral horn that activate excitatory interneurons to motor neurons that innervate extensors and inhibit interneurons to motor neurons that innervate the flexors so that you can swap weight to the other side. 

brain stem: medulla oblongata

• Ventral surface

  • Pyramid: underneath pons. 

  • Olivary eminence

  • The upper open medulla forms the floor of the fourth ventricle

• Dorsal surface

  • Partially covered by cerebrum

• Cranial nerves

  • Glosspharangeal 9

  • Vagus 10

  • Hypoglossal 12

• Transition from spinal cord to brain stem is the pyramidal decussation (crossing midline)

brain stem: pons

• Forms the floor of the fourth ventricle

• Contains fibers connecting to the cerebellum

• Cranial nerves

  • Trigeminal 5

  • Abducens 6

  • Facial 7

  • Vestibulocochlear 8

brain stem: midbrain

• Merges with the diencephalon

• The base of the midbrain contains the Crus Cerebri and the substantia nigra

• The roof of the midbrain contains the tectum 

• Cerebral aqueduct passes through the midbrain.connection between 3rd and 4th ventricles 

• Cranial nerves

  • Oculomotor 3

  • Trochlear 4

brain stem: reticular system

• Diffuse group of neurons within the brain stem. Receives sensory information

• Regulates breathing and heart rate

Olfactory

CN 1.

• Sensory 

• Smell

optic

CN 2. Sensory

Oculomotor

CN 3

• Motor 

• Eye muscles

• Innervates 5 eye muscles 

  • Levator palpebrae superioris

  • Superior rectus

  • Inferior rectus

  • Medial rectus

  • Inferior oblique 

• *Parasympathetic 2 intrinsic 

  • Ciliary muscles and sphincter pupillae muscle 

Trochlear

CN 4

• Motor

• Eye muscles 

• Innervate 1

  • Superior oblique

Trigeminal

CN 5

• Motor and sensory 

• Face and oral cavity

• Ophthalmic (sensory), maxillary (sensory), mandibular (both). 

• Hot and cold, smooth or hard in mouth. NOT taste/special sense. 

Abducens

CN 6

• Motor

• Eye muscles

• Innervates 1

  • Lateral rectus

Facial

CN 7

• Both

• anterior ⅔ tongue. Taste 

• Face and oral cavity

• Motor and sensory 

• Facial expression 

• *Parasympathetic: submandibular and sublingual glands, nasal and oral mucosa, lacrimal glands. 

Vestibulocochlear

CN 8

• Sensory 

• Auditory 

Glossopharyngeal

CN 9

• Both 

• Larynx Pharynx and Tongue

• Posterior ⅓ tongue. Taste and general sensation 

• Innervates one muscle

  • Stylopharyngeus muscles. Lifts throat during swallowing. 

• Sends a nerve to carotid body and carotid sinus 

• *Parasympathetic: parotid gland

Vagus

CN 10

• Both

• Larynx Pharynx and Tongue

• Innervates constrictor muscles of the larynx 

• Sensory of pharynx and larynx 

• *Parasympathetic: lungs liver colon, etc.

Accessory

CN 11

• Motor 

• Spinal cord

• Somatic motor. 

Hypoglossal

CN 12

• Motor 

• Larynx Pharynx and Tongue

• Innervates the intrinsic and extrinsic muscles of the tongue.

What is an upper motor neuron?

AKA primary motor cortex/Precentral gyrus (area 4 of motor cortex) initiation of movement. 

What is a lower motor neuron?

Connect to muscle

List all parts of the direct motor pathway in the correct order.

Where do direct motor fibers decussate?

 Cross midline at the level of motor nucleus they innervate (lower motor neurons, no discrete decussations) innervate head ad neck muscles via the cranial nerves. 

What fibers travel in the genu of the internal capsule?

(Bend) carrying fibers that go to brain stem (corticonuclear). Control muscles of head and neck. Voluntary somatic motor fibers. Precise and voluntary movements. (lower motor neurons = motor nuclei of cranial nerves 5 7 9 12) 

What fibers travel in the posterior limb of the internal capsule?

Carrying motor axons to trunk and extremities. Becomes cruce cerebri. 

What is different between the lateral and ventral corticospinal tracts

Lateral: all fibers have crossed at pyramidal decussation. Innervate lateral neurons of cervical and lumbar enlargements. Motor cortex control of skeletal muscles on teh opposite side of body. Precise voluntary movements of the arms and legs. 

Ventral: have not crossed at pyramidal discuss. Most cross at spinal cord. Motor cortex control of skeletal muscles on both sides of body. Trunk movements.

What are the 3 indirect motor pathways?

Vestibulospinal, Reticulospinal, Tectospinal

Vestibulospinal

• Come from vestibular nuclei in the brainstem. Inner ear contains vestibular apparatus. 

• Origin: vestibular nuclei, pons, medulla 

• CN 8 

• Project to spinal cord

• Regulate reflexive regulation of balance and posture. Gravity.