The Nervous System

2 Types of Nervous Tissue

1. Neurons (Nerve Cells)

2. Neuroglia

Neurons

• also known as Nerve Cells

• are the working units of the nervous system

• generate and transmit nerve impulses

Neuroglia

• type of connective tissue formed by glial cells

• support the neurons

True or False: Neurons can divide

False: Neurons cannot divide, and for survival they need a continuous supply of oxygen and glucose.

Nerves

Bundles of axons bound together

What are action potentials?

Neurons generate and transmit impulses called action potentials.

True or False: Can action potentials be initiated in response to stimuli by either outside the body and/or inside the body?

True

• Outside the body, example touch, light waves

• Inside the body, example a change in the concentration of carbon dioxide in the blood alters respiration.

Parts of a Neuron

• Cell Body

• Axons

• Dendrites

Cell Body

• form the grey matter of the nervous system

• found in the periphery of the brain and in the center of the spinal cord

Nuclei

Groups of Cell bodies (in the CNS)

Ganglia

Groups of cell bodies (in the PNS)

Axons

• carry impulses AWAY from the cell body and are usually much longer than dendrites.

Tracts

• found deeps in the brain and at the periphery of the spinal cord groups of axons.

Dendrites

• short processes that receive and carry incoming action potentials and DIRECT them towards cell bodies.

• same structure as the axons, but are usually shorter and more branching.

The principal Ions involved at The Action Potential (Nerve Impulse)

1. Sodium

2. Potassium

What is the charge of the outside of the nerve cell on the outside and inside when at rest?

At rest, the charge of the nerve cell on the outside is (+) and inside it is (-).

Synapse

The point at which the action potential passes from the presynaptic neuron to the postsynaptic neuron.

Synaptic Knobs or Terminal Boutons

At its free end, the axon of the presynaptic neuron breaks up into minute branches that terminate in small swellings.

Synaptic Cleft

The space between The Synapse and Neurotransmitters

4 types of Neuroglia

1. Astrocytes

2. Oligodendrocytes

3. Ependymal Cells

4. Microglia

Astrocytes

• These cells are the most abundant neuroglia.

• They are star-shaped with fine branching processes.

• are found in large numbers adjacent to blood vessels, with their foot processes forming a sleeve round them.

Blood-brain barrier

The blood is separated from the neurons by the capillary wall and a layer of astrocyte foot processes, which together constitute the blood-brain barrier.

Oligodendrocytes

• These are cells smaller than astrocytes.

• They are found in the clusters round nerve cell bodies in grey matter and are located adjacent to, and along the length of, myelinated nerve fibers.

Oligodendrocytes

form and maintain myelin in the CNS

Schwann Cells

form and maintain myelin in the PNS

Ependymal Cells

• These cells form the epithelial lining of the ventricles of the brain and the central canal of the spinal cord.

• Those cells that form the choroid plexuses of the ventricles secrete cerebrospinal fluid (CSF).

• Some also have cilia that assist the flow of CSF.

Microglia

• The smallest and least numerous glial cells.

• These cells are thought to be derived from monocytes that migrate from the blood into the nervous system before birth.

• They are dispersed throughout the brain.

Types of Nerves

1. Sensory or Afferent Nerves

2. Motor or Efferent Nerves

3. Mixed Nerves

Sensory or Afferent Nerves

• Somatic, cutaneous, or common senses

• Proprioceptor senses

• Special Senses

• Autonomic afferent nerves

Somatic, cutaneous, or common senses

for pain, touch, heat and cold

Proprioceptor Senses

for position of the body and its parts in space thereby enabling maintenance of posture and balance.

Special senses

for sight, hearing, balance, smell and taste

Autonomic afferent nerves

for involuntary activity and visceral pain; found in internal organs, glands, and tissues.

Motor or Efferent Nerves

• Somatic Nerves

• Autonomic nerves (Sympathetic and Parasympathetic)

Somatic Nerves

involved in voluntary reflex and reflex skeletal muscle contraction.

Autonomic nerves (Sympathetic and Parasympathetic)

• involved in cardiac and smooth muscle contraction and glandular secretion.

• for involuntary function

Mixed Nerves

both sensory (afferent) and motor (efferent) in function.

Brain

• Cerebrum

• Diencephalon

  • Thalamus

  • Hypothalamus

• Brain stem

  • Midbrain

  • pons

  • medulla oblongata

• Cerebellum

Cerebrum

• largest part of the brain and it occupies the anterior and middle cranial fossae.

  • higher order functions

  • sensory perception

  • initiation and control of skeletal muscle contraction and therefore voluntary movement.

Thalamus

Involved in arousal, and the processing of some emotions and complex reflexes. It relays and redistributes impulses from most parts of the brain to the cerebral cortex.

Hypothalamus

• It is situated below and in from of the thalamus, immediately above the pituitary gland.

• Controls the output of hormones from both anterior and posterior lobes of the pituitary gland.

• Other functions:

  • effectors of the autonomic nervous system

  • appetite and satiety

  • thirst and water balance

  • body temp.

  • emotional reactions

  • circadian rhythms

Midbrain

The nuclei found in the midbrain acts as relay stations for the ascending and descending nerve fibers and have important roles in auditory and visual reflexes.

Pons

• it processes information from several of the cranial nerves including the 5th cranial nerve and 8th cranial nerve.

• Contains the pneumotaxic area that operates in conjunction with the respiratory center in the medulla oblongata to control respiration.

Medulla Oblongata

The vital centres, consisting of groups of cell bodies (nuclei) associated with autonomic reflex activity, lie in its deeper structure.

These are the:

■ cardiovascular centre

■ respiratory centre

■ reflex centres of vomiting, coughing, sneezing and swallowing

Cerebellum

• It controls and coordinates the movements of various groups of skeletal muscles, ensuring smooth, even and precise actions.

• Cerebellar activity is not under voluntary control.

• It coordinates activities associated with the maintenance of posture, balance and equilibrium.

• It may also have a role in learning and language processing.

Spinal Cord

• The spinal cord is an elongated, almost cylindrical parts of the CNS.

• The spinal cord is the nervous tissue link between the brain and the rest of the body.

• Nerves conveying impulses from the brain to the various organs and tissues descend through the spinal cord.