FUNCTIONAL NEUROANATOMY (Module 1 part 1)

♥INTRODUCTION – BRAIN STRUCTURE & FUNCTION

Today’s topic is functional neuroanatomy

This is a drawing of your nervous system – Note that it resembles the shape of the animal (as seen in this figure) because the structure of the nervous system is intricately tied to its function.

♥OUTLINE

Outline shows topics and goals for today’s lecture

NOTE: There is going to be A LOT of vocabulary you need to become familiar with them.

♥Invertebrate nervous systems

Every organism has some kind of nervous system.

Most organisms fall into one of 2 categories:

  • invertebrate (those with no backbone or spine) or

  • vertebrate (those with a boney structure and a spine)

Ganglia are groups of neurons that work together and in invertebrates, ganglia are typically found around or near the systems they control (like the digestive system)

All vertebrates but only some invertebrates have a brain, but invertebrate brains are “primitive” at best

Arthropods, which include insects, arachnids, and crustaceans, are examples of invertebrates with primitive “brains” or clusters of neurons that control certain functions.

On the cellular level the nervous systems of vertebrates and invertebrates are very similar – with some minor differences.

Vertebrate brains usually have many neurons devoted to information processing,
invertebrate brains usually have fewer but larger neurons to integrate information.

♥Common Features of Vertebrate Nervous Systems

The features shared by all vertebrates include:

  1. Development from a neural tube

  • From the ectodermal germ layer

  • neural crest cells also develop from the ectodermal layer and spread out to become Schwann cells, meninges, adrenal medulla

  • nervous system lies above the digestive system, which lies above the circulatory system

  1. Bilateral symmetry –– although there are some subtle differences between the two sides. There is definitely asymmetry when it comes to hemispheric function

  2. Segmentation – pairs of spinal nerves extend from each level of the spinal cord

  3. Separate systems – certain structures work together to control or produce a behavior or set of behaviors

  4. Localization of function – certain functions are controlled by certain areas.

  5. Hierarchical control – control is organized in a top down fashion 3 levels: cortical, cerebellar, spine

♥DIVISIONS OF THE NERVOUS SYSTEM

2 primary divisions:

  • central nervous system

The central nervous system = brain and spinal cord which are located within the skull and the vertebral column.

  • peripheral nervous system.

peripheral nervous system = is everything else outside of the bony encasement of the skull and vertebral column –

The PNS is further divided into 2 divisions: autonomic nervous system (visceral) and somatic nervous system (somatic includes the cranial nerves and spinal nerves.

The peripheral nerves are distributed to all sense organs, muscles and glands on the surface of the body and to smooth and cardiac muscles and glandular tissues within the body cavity.

The PNS carries sensory information to the CNS (afferents) and carries information from the CNS to the body’s organs, muscles and glands (efferents).

♥︎CNS: Brain and Spinal cord

Intro to Brain and spine

♥︎ CNS: Brain (Cerebral Cortex):

Portion that dominates the surface view is the Cerebral cortex.

Note that it looks like a wrinkled prune

A sulcus is a small groove (plural sulci), and a fissure is a large groove. The bulges between the sulci and fissures are a gyrus (plural gyri)

 

The portion of the brain with the bulges or convolutions is called the cortex (or neocortex)

It is the largest of the 3 sub-divisions of the telencephalon (we will talk more about that later).

The cortex can be divided into 4 lobes named for the skull bones that overlying them:

  • frontal,

  • parietal,

  • occipital, and

  • temporal

anatomical boundaries can be seen between some of them made from the various fissures or sulci.

  • The Central sulcus divides the Frontal and Parietal,

  • The Sylvian or Lateral Fissure divides the Temporal lobe from the frontal and parietal.

  • The division of the occipital lobe is not so obvious and is more of a functional landmark

  • The interhemispheric (medial longitudinal) fissure which separates the 2 hemispheres.

we can generally assign broad categories of behaviors to each lobe, such as:

  • The occipital lobe processes visual information

  • Temporal lobe processes auditory information, and recognizes objects

  • Parietal lobe processes sensory information and spatial information

  • Frontal lobe is important for integrating movement information and processing high level cognitive information

So...the brain evolved gyri and sulci to allow for greater surface area (bigger brain) within the confines of the skull which has to go through the pelvic cavity.

 

♥Comparison of CEREBRAL CORTEX

  • rat brain is essentially void of gyri and sulci –or lissencephalic.

  • Dogs and cats have some convolutions, but are less than that of a non-human primate (monkey or chimp).

  • Non-human Primate brains are not nearly as convoluted as a human brain - but more than a dog or cat.

  • the more complex our behaviors the more isocortex (cortex) )surface area is needed, gyri and sulci allow for increased surface area in same sized spaced

♥︎CNS: SPINE (vertebral Column)

The spine - receives info from the skin, joints, and muscles of the trunk and limbs, and sends out motor commands for movement, both reflexive and voluntary.

It is a bony structure that covers and protects the spinal cord

  • 33 individual bones, make up the vertebral column

cervical (7), thoracic (12), lumbar (5), sacrum (5), and coccyx (4).

the vertebrae of the sacrum and coccyx are fused

provides main support for our bodies, while protecting the spinal cord from injury.

  • intervertebral disks, provide a cushion for the vertebra

Cervical (neck) - the main function of the cervical spine is to support the weight of the head (about 10 pounds). The seven cervical vertebrae are numbered C1 to C7. The neck has the greatest range of motion

Thoracic (mid back) - the main function of the thoracic spine is to hold the rib cage and protect the heart and lungs. The twelve thoracic vertebrae are numbered T1 to T12. The range of motion in the thoracic spine is limited.

Lumbar (low back) - the main function of the lumbar spine is to bear the weight of the body. And for that reason, these vertebrae are much larger in size, to absorb the stress of lifting and carrying heavy objects. The five lumbar vertebrae are numbered L1 to L5.

Sacrum - the main function of the sacrum is to connect the spine to the hip bones. There are five sacral vertebrae, which are fused together.

Coccyx region - the four fused bones of the coccyx or tailbone provide attachment for ligaments and muscles of the pelvis.

♥︎CNS: CNS: SPINE (spinal cord) (1)

The spinal cord is within the column and consists of bundles of cells bodies (neurons) and nerves fibers (the axons or connections) coming from the brain.

protected and covered by meninges.

A cross section of the spinal cord reveals a butterfly-like structure.

 

♥︎CNS: SPINE (spinal cord) (2)

There is a butterfly-shaped area of gray matter surrounded by white matter- in the figure here (in the lower right), because of the stain used, the gray matter looks white and the white matter looks gray or black,

The gray matter consists of cell bodies of motor and sensory neurons

The white matter that surrounds the gray matter is made up of bundles of ascending and descending nerve fibers.

dorsal horn contains sensory neurons

ventral horn contains motor neurons

ventral roots Carry Motor neuron fibers that project out of cord

dorsal roots Carry Sensory fibers information up to brain.

dorsal root ganglion are where cell bodies for these sensory neurons coming from the body are clustered together

The projections of the ventral root and dorsal root come together just beyond the dorsal root ganglion (moving away from the cord) to form a spinal nerve

Sensory information coming from the periphery travels into the spinal cord and up through the brainstem to reach the cortex. The brain sends motor commands down through the brainstem into the spinal cord and out into the periphery,

lateral horn located near the outter edge of the middle of the gray matter contain cell bodies for fibers that go out to the autonomic nervous system.

♥︎ Peripheral nervous system (1)

the peripheral nervous system is everything outside of the central nervous system; has two sub-divisions,

  • somatic nervous system.

    • carries information to and from muscles and information about (5) senses (sight, hearing, taste smell, touch).

  • autonomic nervous system

    • classic subdivisions: sympathetic and parasympathetic- but now is a third: enteric system

the nerves that make up the peripheral nervous system are what come out of the spinal column.

♥︎ Peripheral nervous system (2)

enteric- considered third division of the autonomic nervous system- controls the gastrointestinal system-

♥︎PNS: Somatic Nervous System (SNS)

The somatic nervous system contains nerves that innervate (connect to) skeletal muscle, so this is a voluntary system

It consists of the spinal nerves and the cranial nerves

The somatic nerves are efferents and afferents- so they carry messages that exit and arrive into the brain. And the main transmitter this system used is acetylcholine as it is connecting mainly with skeletal muscle

♥︎PNS: SNS: Spinal nerves

Spinal nerves leave the vertebral column through the intervertebral foramen– small opening in the vertebra

a pair of nerves exit between each vertebra (one on either side).

There are 33 vertebra, but only 31 pairs of spinal nerves,

cervical spinal nerves (C1-C7) are numbered according to the vertebrae that is below it when it exits the spinal cord- (cervical nerve C8 exits between vertebrae C7 and vertebrae Thoracic 1),

The other spinal nerves -12 thoracic nerves (T1 to T12), 5 pairs of lumbar nerves ( L1 to L5), 5 pairs of sacral nerves (S1 to S5), and 1 pair of coccygeal nerves – are numbered according to the vertebrae that is above it when it exits the spinal cord-

The first nerve, C1, does not emerge from the vertebral column– it emerges between the first cervical vertebra and the occipital bone.

All spinal nerves carry BOTH sensory and motor axons (nerve fibers); formed from the fusion of the two branches (the dorsal and ventral nerve roots);

dorsal roots consist of sensory axons and enters the spinal cord as the dorsal nerve root.

ventral roots consist of motor fibers, both somatic and autonomic, emerge as the ventral nerve root.

these combine to form the spinal nerve which then branches out and innervates locations in the body that roughly correspond to the levels they exit from-

cervical nerves innervate areas in the top part of the body,

thoracic nerves innervates areas around the middle of the back and torso.

lumbar and sacral innervates areas around the lower back and torso and legs

(Note: C1 has no dermatome (an area of skin that is innervated by a single spinal nerve) but mostly it carries motor fibers.

coccygeal nerve branches out just around the coccyx or tailbone near the spine so it does not go very far.

♥︎PNS: SNS: Cranial Nerves

Cranial Nerves: second part of the somatic nervous system

similar to the spinal nerves but cranial nerves serve the sensory and motor functions of the head and neck (spinal nerves serve sensory and motor functions of the body)

  • cell bodies lie in the brainstem [except for cranial nerve I (olfactory) which originates in the forebrain, and cranial nerve II (optic nerve) which originates in the thalamus].

  • cranial nerve X: only cranial nerve that does not innervate the head and neck- innervates organs in the periphery (body)

Are 12 pairs of cranial nerves, one left sided and one right sided

These leave and enter small openings in the skull ; do not pass through the spinal cord

Each of the 12 pairs are identified by a name and a roman numeral

Some are pure sensory, some are pure motor and some are both (mixed)

I Olfactory (Smell)--Sensory

II Optic (Sight)- Sensory

III Oculomotor (Moves eyelid and eyeball (upward position) and adjusts the pupil and lens of the eye)- Motor

IV Trochlear (Moves eyeballs inward and downward) - Motor

V Trigeminal (Facial muscles incl. chewing; Facial sensations) -Both

VI Abducens (Moves eyeballs laterally (side to side) - Motor

VII Facial (Taste, tears, saliva, facial expressions) -Both

VIII Vestibulocochlear (Auditory & Balance) - Sensory

IX Glossopharyngeal (Swallowing, saliva, taste) Both

X Vagus (Control of PNS e.g. smooth muscles of GI tract) - Both

XI Accessory (Moving head & shoulders, swallowing) -Motor

XII Hypoglossal (Tongue muscles - speech & swallowing) -Motor

♥︎ PNS: Autonomic Nervous System (ANS)

autonomic system = second division of the peripheral nervous system . This is a non-voluntary or, “automatic” system

3 sub-divisions,

  • sympathetic

  • parasympathetic

  • enteric

nerves of both the sympathetic and parasympathetic systems (classic systems) come from cells within the spinal cord and within the brain stem; efferents send information OUT of the CNS to the visceral parts of the body (e.g. stomach and gastrointestinal system)

Both systems (parasympathetic and sympathetic) talk to many of the same organs, but messages are different due to use of different neurotransmitters (chemicals neurons use to communicate):

sympathetic system releases norepinephrine (also known as noradrenaline)

parasympathetic releases acetylcholine

nerves coming out of the brain and spinal cord, first connect to clusters of neurons called autonomic ganglia (groups of neurons in the periphery of vertebrates = ganglia) and ganglia send connections out to the organs.

connections coming out of the brain and spinal cord to the ganglia are “preganglionic” and the connections or nerves leaving the ganglia to go to the organ are called “post-ganglionic”

♥︎ PNS: ANS: THE SYMPATHETIC SYSTEM

FIGHT OR FLIGHT system; gets your body ready to do things, ready to act: so it speeds up heart rate, increases blood pressure, mobilizes the body's energy stores for emergency and prepares for action.

The cell bodies (neurons) that give rise to the sympathetic division lie in the lateral horn of the thoracic and lumbar regions of the spinal cord. (Thoracolumbar)

Some of the ganglia of the sympathetic division are located in bilateral chains close to the spinal cord (but outside of the vertebral columns), known as the sympathetic trunk or chain.

The rest of the sympathetic ganglia pass through the sympathetic chain to synapse on several collateral ganglia

The one unique organ that does not stop at ganglia is the adrenal gland (medulla). It gets direct innervation because it functions as both an organ and neural tissue–

In the sympathetic system the axons of the preganglionic cells are short because the ganglia lie close to the spinal cord, and these axons release acetylcholine when they connect to ganglion.

The axons leaving the ganglion (postganglionic connections) tend to be long (in contrast to the short preganglionic axons) so they spread out to innervate many organs. It is the postganglionic neurons that release norepinephrine when they reach their target organs

♥︎ PNS: ANS: THE PARASYMPATHETIC SYSTEM

REST and DIGEST system; acts to slow things down and to conserve the body's resources; this system also restores homeostasis: it slows the heart, reduces blood pressure, and prepares the body for relaxation and rest,

neurons that give rise to the parasympathetic system lie in the brain stem nuclei (nuclei = groups of neurons that work together within the CNS) associated with cranial nerves, and in the lateral horn of the sacral region of the spinal cord. (Craniosacral) (Craniosacral)

parasympathetic division does not have a chain of ganglia

nerves coming from the brain and spinal cord connect to ganglion cells that are dispersed throughout the body,

preganglionic cells tend to be long because the ganglia are far from the spinal cord,

postganglionic connections/axon tend to be short and the ganglion tend to be close to the organ they innervate

BOTH the preganglionic axons and post ganglionic axons release acetylcholine.

♥︎ANS: Enteric Nervous System

The enteric nervous system (ENS):

  • considered the third subdivision of the autonomic nervous system (ANS).

  • Is a very extensive network of connected ganglia that directly control the gastrointestinal system (GI system plays a key role in maintaining fluid and nutrient balance)

  • largest and most complex unit of the peripheral nervous system (runs from esophagus (throat) to anal canal)

  • consists of 400-600 million neurons grouped together into ganglia contained within two major networks (plexuses- (a plexus is a system of interconnected and interworking nerves- (ganglia))

    • Myenteric plexus-found mostly in the smooth muscle along the entire length of the GI tract. Regulating the musculature of the gut, such as the tone of the gut and the velocity and intensity of contractions

    • submucosal plexus- lies just beneath the mucosal layer of the gut and is found mostly in the small and large intestines. Involved with local conditions and controls local secretion, absorption, and muscle movements.

gets input from, and sends information to, the CNS via the sympathetic and parasympathetic systems,

but can also perform some behaviors without any input from autonomic system. These include:

  • motor functions, local blood flow, mucosal transport and secretions, and modulation of immune and endocrine functions

scientist are investigating the brain-gut connection because the enteric nervous system may play a role in the development of many pathophysiological or abnormal processes that underlie CNS disease, (connections between the two may provide pathways for diseases that start in the gut to spread to the brain.

  • Some examples: Parkinson’s disease, autistic spectrum disorders, Alzheimer disease, amyotrophic lateral sclerosis (ALS), and varicella zoster virus (VZV) or shingles, mood disorders (anxiety and depression)