CH13

The chapter on the Central Nervous System (CNS) provides an in-depth look at the brain and spinal cord, which form the core of the CNS. Key details include:

  1. Spinal Cord:

    • It serves as a two-way conduction pathway, connecting the brain to peripheral nerves and acting as a center for reflexes.

    • Extends from the brainstem to vertebra L1 or L2, ending in the conus medullaris.

    • Nerve roots, such as the cauda equina, extend beyond the spinal cord, allowing for neural connectivity.

    • The spinal cord has white matter (outer layer, facilitating communication with the brain) and gray matter (shaped like an "H" and involved in motor and sensory functions).

  2. White Matter:

    • Composed of myelinated and unmyelinated axons, classified into ascending, descending, and commissural fibers.

  3. Gray Matter:

    • Divided into somatic sensory (SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM) regions.

    • Contains interneurons (dorsal horns) and motor neurons (ventral/lateral horns).

  4. Brain:

    • Controls complex functions such as intelligence, consciousness, and memory, while also regulating essential functions like heart rate and respiratory rate.

    • Organized into four main regions: cerebral hemispheres, diencephalon, brainstem (including medulla, pons, and midbrain), and cerebellum.

    • Features structures such as ventricles that contain cerebrospinal fluid (CSF), which cushions the brain and spinal cord.

  5. Protection of the CNS:

    • The brain and spinal cord are protected by bones, meninges (dura mater, arachnoid mater, pia mater), and cerebrospinal fluid (CSF).

This chapter highlights the anatomy, organization, and crucial functions of the CNS, emphasizing both structural and functional aspects.

Cerebral Cortex Overview

  • Sensory area for each major sense: Primary sensory cortex

  • Each primary sensory cortex has an association area that processes sensory information:

    • Sensory association areas

  • Multimodal association areas:

    • Receive and integrate input from multiple regions of the cerebral cortex

  • Motor cortex:

    • Plans and initiates voluntary motor functions

Information Processing in the Cerebral Cortex

  • Sensory information received by the primary sensory cortex

  • Information relayed to the sensory association area

  • Multimodal association areas receive input in parallel from sensory areas

  • Motor plan is enacted after processing

Sensory Areas of the Cerebral Cortex

  • Located in parietal, temporal, and occipital lobes

  • Distinct regions interpret different senses

Primary Somatosensory Cortex

  • Located along the postcentral gyrus

  • Involved in conscious awareness of general somatic senses

  • Sensory homunculus: body map of the sensory cortex

  • Projection is contralateral (opposite side of the body)

Somatosensory Association Cortex

  • Located posterior to the primary somatosensory cortex

  • Integrates touch and pressure

  • Recognizes objects without visual input by drawing on past experiences

Visual Areas

  • Primary visual cortex:

    • Located in the calcarine sulcus in the occipital lobe

    • Receives visual info from the retina, contralateral function

  • Visual association area:

    • Processes visual details like color, form, and movement

Auditory Areas

  • Primary auditory cortex:

    • Awareness of sound from the inner ear

    • Located at the superior edge of the temporal lobe

  • Auditory association area:

    • Evaluates sounds

    • Involved in speech recognition (within Wernicke’s area)

Motor Areas of the Cerebral Cortex

  • All motor areas located in the posterior frontal lobe

    • Premotor cortex

    • Primary motor cortex

    • Frontal eye field

    • Broca’s area (speech production)

Primary Motor Cortex

  • Located in the precentral gyrus

  • Controls voluntary motor functions

  • Pyramidal cells send motor signals for skilled movements, contralateral function

Premotor Cortex

  • Located anterior to the precentral gyrus

  • Controls complex movements

  • Involved in planning movements based on sensory feedback

Frontal Eye Field

  • Controls voluntary eye movement, especially when tracking a moving target

Lateralization of Function

  • Left hemisphere:

    • Language, math, logic

  • Right hemisphere:

    • Visual-spatial skills, emotion, intuition, artistic abilities

Cerebral White Matter

  • Commissures: connect hemispheres (largest is the corpus callosum)

  • Association fibers: connect different parts of the same hemisphere

  • Projection fibers: vertical tracts that send signals to/from the cortex

Deep Gray Matter of the Cerebrum

  • Basal ganglia: involved in motor control

  • Basal forebrain nuclei: involved in memory

  • Amygdala: part of the limbic system (emotional brain)

Functional Brain Systems

  • Limbic system: processes emotions, involved in memory

    • Includes structures like the amygdala, hippocampus, and cingulate gyrus

  • Reticular formation: spans the brainstem, involved in alertness

Protection of the Brain

  • Dura mater: strongest meninge, protects the brain

  • Cerebrospinal fluid (CSF): formed by the choroid plexus, circulates around the brain and spinal cord to provide protection and nutrient transport.