7 - The Central Nervous System (CNS)

Gray Matter

unmyelinated nerve cell bodies, dendrites, and axons

White Matter

mostly myelinated axons + contains very few neuronal cell bodies

• its pale colour comes from the myelin sheaths that surrounds the axons

Tracts

bundles of axons that connect different regions of the CNS

Meninges

consists of 3 layers of connected tissue with fluid between them

• Dura Mater

• Arachnoid membrane

• Pia Mater

Dura Mater

the outermost and thickest layer of the meninges

• Associated with veins that drain blood from the brain through vessels or cavities called sinuses

Arachnoid Membrane

the middle layer of the meninges

• loosely tied to the inner membrane, leaving subarachnoid spaces between the two layers

Pia Mater

the thinner/smaller inner membrane of the meninges

• Adheres to the surface of the brain + spinal cord

• Arteries that supply the brain are associated with this layer

Extracellular Fluid

final protective compartment of CNS; helps cushion the delicate neural tissue

• Consists of cerebral spinal fluid (found in ventricles + in the space between the pia mater and arachnoid space) and interstitial fluid (lies inside the pia mater)

  • Both compartments communicate with each other across leaky junctions

Central portion of spinal cord contains mainly white or grey matter?

Grey unmyelinated neurons

Outer portion of spinal cord contains mainly white or grey matter?

White myelinated neurons

Dorsal Root (spinal cord)

carries incoming sensory info

Ventral Root (spinal cord)

carries info from CNS to muscles/glands; carry efferent signals

Spinal reflexes do not require sending information to the brain; T or F?

True

Metabolic Requirement of the brain

• Constant supply of O₂ + glucose to make ATP

  • Glucose main source of energy

  • Hypoglycemia (low blood sugar) leads to confusion, unconsciousness, and death

• 15% of blood pumped by heart goes to the brain

Components of the Hindbrain

• Medulla (oblongata)

• Pons

• Cerebellum

Medulla (Oblongata)

• Controls heart rate & respiration

• Thoroughfare (road) for sensory info

• Contains:

  • Somatosensory tracts: brain sensory info to brain

  • Corticospinal tracts: convey info from cerebellum to spinal cord

• Neurons cross over (signals coming from left part of brain controls right side of body, vise versa)

• Area postrema lacks blood-brain-barrier (BBB) to induce vomiting

Pons

Regulates sleep and arousal (alertness)

Cerebellum

Coordinates fine muscle movement & balance

Midbrain

• Important for visual and auditory processes

• Contains reticular formation

  • Sleep + arousal (attention)

  • Connects lower + higher brain centres

• Hypothalamus

• Thalamus

• Pituitary Gland

Thalamus

Sensory switchboard; routes sensory info to its appropriate place

• E.g. visual info goes to visual centres, auditory info to auditory centres, etc.

Hypothalamus

Main controlling centre for autonomic functions (biological drives)

• E.g. sex, temperature, eating, drinking, aggression, emotion

Pituitary Gland

Master gland;

• Sexual development + behaviour

• Metabolism

• Stress

Hypothalamic-hypophyseal portal system

• Hormones released from the hypothalamus into capillaries, delivered to pituitary

• NO BBB

• Blood goes to the gland but doesn’t return back to the heart

Cerebral Grey Matter (Forebrain)

involved in conscious perception + voluntary motor control

3 major regions

• Cerebral cortex

• Basal ganglia

• Limbic system

Cerebral Cortex

• Very thin (3mm thick)

• Convoluted (folded + wrinkled) structure enables more tissue to fit

• Provides flexibility in behaviour

• Controls higher brain functions

Basal Ganglia

• Critical for motor control

• Deliberate initiation of movement

• Part of the forebrain

The Limbic System

• Most primal part of the brain

• Part of the forebrain

• Includes:

  • Hippocampus: forms & retrieves memories

  • Amygdala: fear & aggression

  • Nucleus Accumbens: reward & motivation centre

Corpus Callosum

Allows for communication between both sides of the brain

• Made up of white matter - (myelinated to transfer info)

Simple Pathway in the CNS

Complex Pathway in the CNS

Systems that Influence Output

1. The sensory system - monitors the internal & external environments & external environments and initiates reflex responses

2. A cognitive system - resides in the cerebral cortex & is able to initiate voluntary responses

3. A behavioural state system - also resides in the brain & governs sleep-wake cycles and other intrinsic behaviors

Motor Cortex

• Controls movement on opposite side of the body

• Controls movement of over 600 voluntary muscles

• Located @ rear of frontal lobe

Somatosensory Cortex

• Receives specific sense information from opposite side of body

• At least one specific area for each sense

• Located in parietal lobe

CNS & Motor System

Efferent division of the nervous system

1. Skeletal muscle movement (somatic motor division)

2. Neuroendocrine signals (hypothalamus & adrenal medulla)

3. Visceral responses (autonomic division - smooth & cardiac muscle; endocrine/exocrine glands)

Functional Areas of the Cerebral Cortex

1. Sensory areas: receive sensory input & translate it into perception

2. Motor areas: direct skeletal muscle movement

3. Association areas: integrate info from sensory & motor areas in order to direct voluntary behaviours