Nervous System Lecture Notes

Nervous System

Central Nervous System (CNS)

• Composed of the brain and spinal cord.

Peripheral Nervous System (PNS)

• Composed of cranial nerves and spinal nerves.

Fiber Bundles

• In PNS: Called nerves.
• In CNS: Called tracts.

Divisions of the PNS

• Somatic Nervous System: The voluntary division.
• Autonomic Nervous System: The involuntary division.

Functional Cells

• Neurons: The functional cells of the nervous system.

Neuron Structure

• Dendrites: Carry impulses to the cell body.
• Axons: Carry impulses away from the cell body.

Functional Neuron Types

• Sensory (Afferent) Neurons: Conduct impulses to the spinal cord and brain.
• Motor (Efferent) Neurons: Conduct impulses from the CNS to muscles and glands.
• Interneurons: Relay information from place to place within the CNS.

Myelin Sheath

• In PNS: Formed by Schwann cells.
• In CNS: Formed by oligodendrocytes.

Synapse

• The junction point for transmitting nerve impulses from one neuron to another cell.

Spinal Cord Tracts

• Ascending Tracts: Sensory impulses entering the spinal cord.
• Descending Tracts: Motor impulses traveling from the brain toward the PNS.

Visceral Responses

• The branch of the human nervous system that carries out automatic and unconscious visceral responses.

Sympathetic Nervous System

• Described as "fight or flight".

Parasympathetic Nervous System

• Described as "rest and digest".

Neurotransmitters and Receptors

• Sympathetic Nervous System: Referred to as adrenergic because it is activated by adrenaline.
• Parasympathetic Nervous System: Referred to as cholinergic because its neurons release the neurotransmitter acetylcholine (ACh).
• Neurotransmitter Release: Neurons in the sympathetic nervous system release the neurotransmitter norepinephrine.
• Muscarinic Receptors: Affect parasympathetic responses.

Common Neurotransmitters

• Norepinephrine, serotonin, dopamine, and acetylcholine.

Brain Structures

• Cerebrum: The largest and most superior portion of the brain.
• Diencephalon: Lies between the cerebrum and the brain stem; houses the hypothalamus and pituitary gland.
• Brain Stem: Spans the region between the diencephalon and the spinal cord.
• Pons: Connects the cerebellum with other portions of the brain and helps regulate respiration.
• Medulla Oblongata: Sits between the pons and the spinal cord and links the brain with the spinal cord; contains centers for controlling vital functions such as respiration and heartbeat.
• Cerebellum: Sits below the posterior portion of the cerebrum and coordinates voluntary muscles, maintains balance and muscle tone.
• Midbrain: Connects the cerebrum and diencephalon with the spinal cord; contains reflex centers concerned with vision and hearing; connects the cerebrum with lower portions of the brain.

Meninges

• Structure: Consists of 3 layers of connective tissue that surround both the brain and the spinal cord to form a complete enclosure.
• Pia Mater: Attached to the nervous tissue of the brain and spinal cord, following all contours; delicate connective tissue and the innermost layer.
• Arachnoid Mater: The middle layer of the 3 layers of connective tissue; blood vessels pass through this space.