Nervous System Overview

Nervous System Organization

• The nervous system collects information from the internal and external environment, processes it, and initiates appropriate responses.
• It has three main functions:
  • Monitor sensory input: Sensory neurons detect changes (stimuli) inside and outside the body.
  • Integration: Interneurons process sensory information and initiate responses.
  • Motor output: Motor neurons send signals to muscles or glands to respond to stimuli.

Nervous System Divisions

• Central Nervous System (CNS): Includes the brain and spinal cord.
  • Input: Receives information from sensory organs.
  • Output: Sends signals to muscles and glands.
• Peripheral Nervous System (PNS): Connects the CNS to the rest of the body.
  • Somatic nervous system: Controls voluntary movements of skeletal muscles.
  • Autonomic nervous system: Controls involuntary actions like heart rate and digestion.
    • Sympathetic: Prepares the body for vigorous activity.
    • Parasympathetic: Calms the body and conserves energy.
• Sensory (Afferent): Carries signals towards the CNS.
• Motor (Efferent): Carries signals away from the CNS.

CNS Protection

• Bone: Cranium (skull) and vertebral column protect the brain and spinal cord.
• Connective Tissue (Meninges): Three layered membranes (dura mater, arachnoid mater, pia mater) surround the brain and spinal cord.
• Fluid (Cerebrospinal Fluid, CSF): Bathes the brain and spinal cord, providing nutrients and removing waste.

CNS Homeostasis and Blood-Brain Barrier

• Cerebrospinal fluid (CSF) is produced, circulated, and absorbed into the venous system.
• Sites of production include the choroid plexus in the ventricles.
• CSF provides buoyancy, removes waste products, and is maintained by a balance of its production and reabsorption.
• The blood-brain barrier (BBB) is a protective mechanism preventing harmful substances from entering the brain.
• It's composed of tight junctions between endothelial cells of brain capillaries.

Cerebral Hemispheres

• The cerebral hemispheres (left and right) make up 83% of the brain's mass.
• They contain ridges (gyri) and grooves (sulci).
• They are separated by the longitudinal fissure.
• Each hemisphere has 3 basic regions: cerebral cortex (gray matter), white matter, and basal nuclei.

Cerebral Lobes

• Deep sulci divide the hemispheres into 5 lobes: frontal, parietal, temporal, occipital, and insula.

Cerebral Cortex

• The cerebral cortex is the outermost layer of the brain.
• It accounts for 40% of the brain's mass.
• It's responsible for higher-level functions like sensation, communication, memory, understanding, and voluntary movements.
• Each hemisphere controls the opposite side of the body (contralateral).
• Hemispheres are not equal in function.

Functional Areas of Cerebral Cortex

• The cerebral cortex has three types of functional areas: motor, sensory, and association areas.
  • Motor areas: control voluntary movement.
  • Sensory areas: receive and process sensory information.
  • Association areas: integrate and process information.

Specific Functional Areas (Examples)

• Primary motor cortex: initiate voluntary movement.
• Premotor cortex: coordinate voluntary movements.
• Prefrontal association areas: planning, thoughts, personality.
• Primary somatosensory cortex: sensory input (touch, pressure, temperature).
• Visual association areas: higher-level visual processing.
• Primary visual cortex: initial visual input.
• Auditory association areas: interpret sounds.
• Primary auditory cortex: initial auditory input.
• Wernicke's area: language comprehension.
• Broca's area: speech formation.

Homunculus

• The amount of cortex devoted to a specific body part correlates with the sensitivity or control needed.
• Parts receiving frequent sensory input or requiring complex movement have a proportionally larger cortical area.

Sensory Areas

• Primary somatosensory cortex: Receives information from skin and skeletal muscles.
• Somatosensory association cortex: Processes sensory input.
• Visual areas: Receives visual information from the eye.
• Auditory areas: Receives sound information.
• Olfactory, gustatory, and vestibular cortices: Responsible for smell, taste, and balance, respectively.

Brain Matter

• Cerebral white matter: Composed primarily of myelinated neurons for fast communication.
• Cerebral gray matter: Contains mainly non-myelinated neurons (such as interneurons) and axon cell bodies for sensory and motor processing.

Gray vs. White Matter

• Gray matter: 40% of the CNS, contains interneurons, synapses.
• White matter: 60% of the CNS, contains myelinated axons.