Organization of the Brain (L9)

Nervous System:

1. Fundamental task is to communicate and process information

2. Composed of neurons that carry information (100 billion) and glial cell that support, insulate and nourish neurons (one trillion)

3. Conveys information via electrical and chemical signals

4. The central nervous system (CNS)

5. The peripheral nervous system (PNS)

The central nervous system (CNS)

brain and spinal cord

The peripheral nervous system (PNS)

sensory (afferent) and motor (efferent) nerves

Central Nervous System (CNS): parts

1. Cerebral Hemispheres:

2. Cerebellum:

3. Brainstem

4. Spinal Cord:

Cerebral Hemispheres:

Higher cognitive functions (thoughts and actions)

Cerebellum:

Coordinates execution of movement, posture, and balance

Brainstem

Unconscious body functions (breathing, heartbeat, blood pressure)

Spinal Cord:

Pathway of information between the brain and periphery

Lobes of the Cerebral Cortex:

• occipital

• temporal

• frontal

• parietal

occipital

vision processing

temporal

hearing, learning, memory, and emotion

frontal

planning future action, control of movement

parietal

somatic sensation, relating body image with extrapersonal space

Corpus Callosum:

1.  a thick bundle of myelinated nerve fibers (200 million axons) that connects the right and left hemispheres 

2. A combination of sensory, motor, and cognitive information is constantly being transferred between hemispheres

Cranial Nerves:

1. 12 pairs of peripheral nerves that emerge primarily from the brainstem (CN I is the exception)

2. Carry sensory (balance, taste, smell, vision) and motor information

3. Some motor control is voluntary (for example, eye and tongue movement) some involuntary (pupil constriction)

Optic nerve

sensory → visual receptors

Vestivulocochlear

sensory → information from the inner ear

Spinal Cord:

1. Continuous with the caudal portion of the medulla (brainstem)

2. Consists of 31 segments that each have a motor and sensory root

3. Divided into four regions: cervical (C1-8), Thoracic (T1-12), Lumbar (L1-5), and Sacral (S1-5)

spinal nerves: dorsal (back) root:

• collection of axons that carry incoming sensory information to the CNS (ascending)

•  contains the cell bodies of the nerves that make up the dorsal root. Cell bodies for the ventral root are located in the ventral horns of the spinal cord’s central grey region.

spinal nerves: ventral (front) root:

collection of axons that carry information from CNS to muscles/gland (descending)

Peripheral Nervous System:

1. Traduces physical or chemical stimuli from internal or external sources into sensory information

2. Conveys sensory (afferent) information to the CNS

3. Conveys motor signals from CNS to target organs (primarily muscles)

4. Converts motor signals (efferent) to chemical signals at synapses on target tissues in the periphery 

5. Spinal reflex arc illustrates the functions of the PNS: transduce stimulus, convey information to CNS, convey CNS information to muscle, convert electrical signal to chemical signal at synapses 

6. Compromised of the cranial and spinal nerves, their associated ganglia (cluster of nerve bodies) and sensory receptors

7. Can be divided into somatic and sensory receptors

Gray and White Matter:

1. Tracks of axons are spatially separated, convey different information: 

   1. Ascending tracts (orange segments): convey information from the periphery to the CNS

   2. Descending tracts (teal segments): convey information from the cerebral cortex and brainstem to control motor neurons 

white matter

axon tracts (myelination)

gray matter

mostly everything else (cell bodies, dendrites)

the meninges

1. Three membranes that surround the brain and spinal cord:

   1. Pia mater: thin innermost layer of connective tissue

   2. Arachnoid membrane: middle layer that creates the subarachnoid space

   3. Dura mater: thick connective tissue, inelastic outermost layer that forms a protective envelope

2. The cerebrospinal fluid (CSF, a colorless watery liquid that buffers the brain from mechanical injury) circulates within the subarachnoid space located between the Pia Mater and Arachnoid Membrane

The blood brain barrier:

1. The blood brain barrier protects the brain from internal irritants in blood 

2. Blood capillaries are normally made of endothelial cells that wrap around and form tight junctions with themselves and one another

3. In the brain, these cells are surrounded by glial cells that make it harder for substances to “leak” from the blood into the brain (eg, large molecules, toxins)

4. Tight junctions allow many gases to pass (Eg, O2, CO2)

5. carrier -mediate transporters are present for the transportation of molecules (eg, ions, glucose) into the brain

6. If a drug can cross the barrier can give it in a low dose (eg, Prozac). Increase dosage with increasing difficult (side effects) 

Peripheral nervous system:

1. Compromised of the cranial and spinal nerves, their associated ganglia (cluster of nerve bodies) and sensory receptors

2. Can be divided into somatic and autonomic receptors

Somatic receptors

sensory neurons that innervate the skin, joints, and muscles, as well as the motor axons of skeletal muscles. Primarily deals with the external environment, either to gather information or interact through movement

Autonomic receptors

1. Also called the visceral nervous system: controls the contraction and secretion of various internal organs (smooth and cardiac muscle, glands, and some adipose (fat) tissue)

2. Divided into two divisions based on organization, neurotransmitters and receptors:

3. Sympathetic Division

4. Parasympathetic division

5. Many organs receive input from both divisions. Common to find antagonistic control over a single target: example, one speeds up heart rate, the other slows down the rate.

sympathetic division

Control fight or flight functions

Parasympathetic division:

control rest digest functions

Overview of different nervous systems: