Nervous System - Lecture Notes

Nervous System: Function

Detects impulses from the senses; control center

Primary Functions: Sensory input

Detects stimuli from the environment and internal conditions

Primary Functions: Integration

processes and interprets sensory information

Primary Functions: Motor output

activates muscles and glands in response to stimuli

Nervous System: Major Organs

• Brain

• Spinal Cord

• Senses

• Nerves

Major Components: The Brain

Primary control center for processing information

Major Components: Spinal Cord

a conduit for signals between the brain and the body

Major Components: Peripheral nerves

link the CNS to sensory receptors, muscles, and glands

Major Components: Sensory Organs

Include eyes, ears, taste buds, and olfactory receptors

How is the nervous system organized?

• Central Nervous System (CNS)

• Peripheral Nervous System (PNS)

  • Cranial Nerves

  • Spinal Nerves

• The peripheral nervous system is then further divded

What are the types of nerve cells?

• Neurons - conduct impulses around the body (make up only 10% of the nerve cells)

  • Neuroglia (nerve glue) - support, insulate & protect neurons (90% of nerve cells)

What is the structure of a neuron

• Neurons have different structures, but have a main cell body with processes extending outward

• The cell body contains the nucleus, cytoplasm & organelles

Processes are divided into:

• Dendrites

• Axons

  • At the end of axons are axon terminals, which release neurotransmitters to pass impulses to the next neuron

How is a nerve impulse passed along a neuron?

• A nerve impulse is an electrical signal that travels along the neuron

• It arises from the movement of ions, causing a change in electrical charges

• Key principle: Nerve impulses are all-or-none; the neuron either fires completely or not at all

Electrical Signaling: Resting Potential

• The neuron’s membrane is polarized

  • Intracellular space is negatively charged

  • Extracellular space is positively charged

Electrical Signaling: Depolarization (action potential)

• When the neuron is stimulated, either by the environment or another neuron:

  • Sodium (Na⁺) rushes into the neuron and reverses the charges

Electrical Signaling: Repolarization

• As impulses passes

  • Potassium (K⁺) flows out, restoring resting potential

Electrical Signaling: Sodium-potassium pump

Actively restores the ion concentrations to normal, and the resting potential returns

Synaptic Transmission

• Neurons communicate at synapses, where the axon terminal of one neuron meets the dendrite or soma of another

• Neurotransmitters transmit signals across the synaptic cleft, enabling communication between neurons

Synaptic Transmission Steps:

1. Action potential reaches the presynaptic terminal

2. Voltage-gated Ca²⁺ channels open

3. Neurotransmitters are released from synaptic vesicles

4. Neurotransmitters bind to postsynaptic receptors

5. Sodium channels open, triggering an action potential in the next neuron

Protection of the Central Nervous System

• Three connective tissue layers surround the brain and spinal cord:

  • Dura mater: Tough, outermost layer

  • Arachnoid mater: Thin, web-like middle layer

  • Pia mater: Delicate inner layer, highly vascularized

Cerebrospinal Fluid (CSF)

• Found in the subarachnoid space (between the arachnoid layer and the pia mater)

• Cushions the CNS, maintains homeostasis, and prevents infection

• Produced by choroid plexuses in the ventricles

  • Lateral ventricles (right and left) → Third ventricle → Fourth ventricle.

• Reabsorbed into the bloodstream via arachnoid granulations.

How is the Cerebrospinal Fluid produced

• The CSF is produced in spaces within the brain called ventricles.

  • There are 4 ventricles: 2 lateral ventricles (right & left), third ventricle & fourth ventricle.

  • The lateral ventricles are connected to the third ventricle by the thin interventricular foramen (foramen of Monro).

Structure of the Brain: Cerebrum

• Largest brain region, divided into right and left hemispheres connected by the corpus callosum

• The surface is covered by

  • Gyri: ridges

  • Sulci: Shallow grooves

  • Fissures: Deep grooves separating lobes

3 Major Layers of the Brain

From Superficial to Deep

1. Cerebral Cortex: gray matter; cell bodies, dendrites; processes information

2. Cerebral Medulla: white matter; myelinated axons; transmits signals

3. Basal Nuclei: Control voluntary movements and motor planning

Lobes of the cerebrum: Frontal Lobe

Controls:

• Voluntary movements (walking)

• Reasoning & decision-making

• Memory

• Ability to predict consequences of actions

• Planning

• Verbal communication, specifically in Broca’s area

Lobes of the cerebrum: Parietal Lobe

Separated from the frontal lobe by the central sulcus

Controls:

• Sensations (pain, temperature, touch)

• Visual-spatial processing

• Body position

Lobes of the cerebrum: Occipital Lobe

Controls:

• Visual processing

• Memory of objects

Lobes of the cerebrum: Temporal Lobe

Separated from the frontal lobe by the lateral sulcus

Controls:

• Memory

• Comprehension & pronunciation of works

• Sensations of smell and sound

• Emotional association of memories

Structure of Diencephalon

• Located beneath the cerebrum, small nondescript region

• It contains the thalamus, the hypothalamus, and the pineal gland

Diencephalon: The Thalamus

Relay center for sensory information to the cortex

Diencephalon: The Hypothalamus

Controls:

• Autonomic process (temperature, blood pressure, metabolism)

• Controls hormones released by the pituitary gland

• Part of the limbic system, regulates emotions and feelings of pleasure (hunger, thirst, sex, pain)

Brain Stem Structure

• Located between the cerebrum and the spinal cord

• It is broken into three regions: the midbrain, pons, and medulla oblongata

Brain Stem: The Midbrain

• Also known as the mesencephalon

• Relays information to cerebrum

• Controls body movements and posture

Brain Stem: The Pons

• Almost completely made of white matter that links the cerebral cortex and the cerebellum

• Carries information from one side of the brain to the other

• Central control of breathing

Brain Stem: The Medulla

• The medulla oblongata is located just above the spinal cord.

• Transmits impulses between the spinal cord and the brain.

• Controls blood pressure, heart rate, swallowing, and coughing

Function of the Cerebellum

• Found near the back of the skull; its the second largest part of the brain

• Coordinates voluntary movement for smooth, efficient motion.

• Involved in motor learning and muscle memory.

• Ensures movements are precise and balanced.

Structure of the Spinal Cord

• Extends from the medulla oblongata to the lumbar vertebrae

• Protected by meninges and the vertebral column

• Contains 31 pairs of spinal nerves

• Gray matter forms a “butterfly” shape, surrounded by white matter

Function of the Spinal Cord

• The dorsal horns receive impulses from afferent nerves, then pass the impulses through the ventral horns to the efferent nerves

• Dorsal and ventral roots merge to form spinal nerves

How does the Reflex Arc travel?

• Reflex is a rapid, involuntary response to a stimulus

• Pathway (reflex arc):
  1. Receptor
  2. Sensory neuron
  3. Integration Center (CNS)
  4. Motor neuron
  5. Effector

Types of Reflex Arcs

• Somatic reflexes: Involve skeletal muscles.

• Autonomic reflexes: Involve smooth or cardiac muscle and glands