Nervous System: Anatomy and Physiology

• Overview of the nervous system topics include:
  • Homeostasis & Feedback Mechanism
  • Histology of neurons & neuroglia
  • Physiology of generating a nerve impulse
  • Anatomy & Physiology of the Central Nervous System (CNS) and homeostatic imbalances
  • Anatomy & Physiology of the Peripheral Nervous System (PNS) and homeostatic imbalances

Homeostasis and the Nervous System

• Sensory input is carried to the CNS
• Decisions are integrated
• Motor output is then carried to the PNS

Parts of a Neuron

• Parts of a neuron include cell body, dendrites, axon, and nodes of ranvier
• The cell body contains the nucleus, mitochondria, endoplasmic reticulum, and golgi apparatus
• Dendrites conduct impulses toward the cell body
• Axons conduct impulses away from the cell body
• The Nodes of Ranvier are spaces between two Schwann cells

Histology of Neuroglia

• Neuroglia are also known as glial cells
• Glial cells assist neurons to work efficiently
• The CNS contains 4 types of neuroglia, while the PNS has 2.
• Neuroglia make up 50% of the brain mass with a 10:1 ratio
• Glial cells have a eukaryotic anatomy

Physiology of Neuroglia in the CNS

• Astrocytes brace neurons, form barriers between capillaries and neurons, and control the chemical environment of the brain
• Microglia dispose of debris
• Ependymal cells circulate cerebrospinal fluid (CSF)
• Oligodendrocytes produce myelin sheaths to protect and electrically insulate fibers, which increases the transmission of nerve impulses

Physiology of Neuroglia in the PNS

• Satellite cells function like astrocytes in the CNS
• Satellite cells protect the cell body of the neuron.
• Schwann cells function like oligodendrocytes and form myelin sheaths around larger nerve fibers
• Schwann cells are vital in regenerating damaged nerve fibers in the PNS

Biological Concepts to Review

• Review concepts of Eukaryotic cells, cell membranes, concentration gradients, and types of diffusion
• Types of diffusion include Simple, Facilitated and Active
• Interpret Line Graphs

Action Potential

• Action potential occurs on the axon
• Resting potential
• Depolarization
• Repolarization
• Hyperpolarization
• Action potential occurs multiple times across the axon
• It takes 2-3 milliseconds for the process to complete

Membrane Potential

• Membrane potential refers the electrical difference between the inside and outside of a neuron
• It can be measured in a line graph
  • x-axis: Time (ms)
  • y axis: Membrane Potential (mV)

Resting Potential

• Resting potential occurs when a neuron is not firing an action potential
• Resting potential= -70 mV
• Inner Na+ door is open during resting potential
• Outer Na+ and K+ door is closed

Depolarization

• The electrical impulse ascends during depolarization
• All of the Na+ doors open, causing a rush of ions into the cell
• OUTER Na+ door closes and opens the K+ door, which causes K+ to leak out of the neuron
• The INSIDE Na+ closes after a time

Neurotransmitters

• Depolarization deposits neurotransmitters
• These neurotransmitters are chemicals that dendrites of the next neuron receives
• Action potential repeats following the deposit of neurotransmitters

Repolarization

• K+ leaves the cell, which makes the membrane potential more negative
• OUTER Na+ door closes and INNER door opens during repolarization
• During repolarization, a neuron is returning to resting potential

Hyperpolarization

• K+ channels stay open the longest during hyperpolarization.
• The resting level dips below -70 mV
• That action occurs until the K+ doors are fully closed, returning to resting levels

Choices

• Choices are made on a chemical level
• Neurotransmitters = options
• The closer you are to your decision, the greater amount neurotransmitters are made
• More neurotransmitters = more dendritic spines
• A path of neurons are stored as experience

Anatomy & Physiology of the CNS

• The cerebral hemispheres are the superior part of the brain, made up of 5 lobes
• Frontal, Parietal, Occipital, Temporal lobes and insula
• The insula is covered by other lobes
• There are 3 layers in the brain, from superficial to deep: Gray matter, white matter, basal nuclei

Gray vs. White Matter

• Parts of the neuron are separated into gray or white matter in the brain
• Gray: cell bodies, dendrites
• White: axon, myelinated fibers

Brain Anatomy: Gyri vs Sulci

• Gyri: (gyrus=1) elevated ridges of neural tissue that mark the entire surface of the cerebral hemispheres
• Sulci: (sulcus=1) Shallow grooves; a fissure are very deep sulcus separating major regions
• Knob: a protruding ‘knob-like' shape indicate a talent

Cerebral Cortex

• Cerebral cortex has three parts: motor, sensory & association
• Anatomy: grey matter (cell body, dendrite, glial cell, blood vessel)
• Physiology involves conscious mind, communication, memory, and comprehension

Motor Areas - Anatomy

• Posterior part of the frontal lobes
  • Includes primary motor cortex, premotor cortex, Broca's area and frontal eye field

Motor Areas- Physiology

• Motor areas control voluntary movement with organized skeletal muscles involved in 1 action
• Controls learned motor skills (typing)
• Speech
• Controls extrinsic eye muscles

Homeostatic Imbalance of Motor Area

• Primary motor cortex: paralysis occurs
• Premotor cortex: slower speed in executing task

Sensory Areas

• Anatomy: Parietal, temporal, occipital lobes and insular
  • Includes visual, auditory, olfactory, gustatory, visceral and vestibular senses
• Physiology: conscious awareness of sensation

Homeostatic Imbalance of Sensory Area

• Primary visual cortex imbalance: blindness results
• Visual association area imbalance: lack of comprehension results

Association Areas

• Anatomy: prefrontal cortex, temporal lobe, parahippocampal gyrus
• Physiology: ability to comprehend the sensory input, integrates and responds for homeostasis

Homeostatic Imbalance- Association Areas

• Tumors/lesions can cause imbalance
  • Anterior: loss of judgement, attentiveness, inhibitions
  • Posterior: loss of awareness of self (personal hygiene)

Brain Anatomy: Diencephalon

• Thalamus: receives sensory info to cerebral cortex
• Hypothalamus: body temp, autonomic nervous system
• Epithalamus: secretes melatonin

Brain Anatomy: Brain Stem

• Midbrain
• Pons: Controls breathing
• Medulla Oblongata: controls vomit, hiccup, swallow, cough and sneeze

Brain Anatomy: Cerebellum

• Controls balance in the inner ear, eye and skeletal muscles

Protecting the Brain

• Meninges: Dura Mater, Arachnoid, Pia Mater
• Cerebrospinal fluid
• Blood-Brain Barrier