Chapter 8: Brain and Spinal Chord

Brain and Spinal Cord

• Overview of the central nervous system (CNS) which includes the brain and spinal cord.

• Includes cranial and spinal nerves.

Brain

Four Regions of the Brain

1. Cerebrum

2. Diencephalon

3. Cerebellum

4. Brainstem

Cerebrum

• Structure: Divided into two hemispheres.

• Contains Gyri and Sulci which increase surface area and allow for more neurons.

• Functions include Thinking and Reasoning.

• Contains four lobes:

  1. Frontal lobe

  2. Parietal lobe

  3. Temporal lobe

  4. Occipital lobe

Cerebral Cortex

• Gray matter:

  • Comprises 75% of all neuron cell bodies, dendrites, and interneurons.

  • Unmyelinated.

• White matter:

  • Bulk of cerebrum consisting of bundles of myelinated axons (tracts).

  • Continuous with the spinal cord.

Diencephalon

• Components:

  • Thalamus: Acts as a gatekeeper for sensory and motor neurons.

  • Hypothalamus: Maintains Homeostasis—regulates body temperature, hunger, thirst, sexual pleasure, rage, fear, relaxation, and controls the autonomic nervous system and stimulates the pituitary gland.

  • Epithalamus: Involved in emotional responses to odors and the onset of puberty.

Brainstem

• Structures include Midbrain, Pons, and Medulla Oblongata.

• Functions:

  • Pons: Acts as a bridge between various parts of the nervous system; helps in regulating respiratory functions.

  • Medulla Oblongata: Handles vital functions such as consciousness, cardiovascular regulation, and reflex actions like coughing and swallowing.

Cerebellum

• Functions:

  • Maintaining balance, posture, and muscle tone during fine motor movements.

  • Facilitates smooth and coordinated motion.

  • Plays a role in motor learning of new tasks and operates subconsciously.

The Limbic System

• Consists of:

  • Hippocampus: Involved in memory formation (long-term from short-term).

  • Amygdala: Associated with emotion processing, located in the temporal lobe.

  • Basal Ganglia: Involved in movement and reward pathways.

  • Thalamus: Functions as a sensory gateway.

Memory

• Categories of Memory:

  • Sensory Memory: Memories recalled via sensory cues.

  • Motor Memory: Related to skills, including fine and gross motor skills.

  • Visuospatial Memory: Involves understanding the spatial relationship between objects and their visual representation.

  • Language Memory: Ability to associate words with objects and use them in communication.

Meninges, Ventricles, & Cerebrospinal Fluid (CSF)

• Meninges: Three connective tissue membranes wrapping the CNS.

  1. Dura Mater: Outermost layer, tough and protective.

  2. Arachnoid Mater: Middle layer, web-like appearance.

  3. Pia Mater: Innermost layer, delicate and adheres closely to the brain and spinal cord.

• Important regions include:

  • Dural venous sinuses: Venous drainage channels.

  • Subdural space: Space between dura mater and arachnoid mater.

  • Subarachnoid space: Contains CSF and blood vessels.

Ventricles

• Function: Create and circulate CSF.

• Four Ventricles:

  1. Lateral Ventricles (anterior horn)

  2. Third Ventricle

  3. Lateral Ventricles (inferior and posterior horns)

  4. Fourth Ventricle

• Additional features:

  • Cerebral Aqueduct: Channel connecting the third and fourth ventricles.

  • Central Canal: Extends through the spinal cord.

The Spinal Cord

• Nerve roots exits locations and general overview of the spinal cord anatomy.

• Levels:

  • C1 to S5 segments.

  • Cauda Equina: Bundle of spinal nerves extending from the lower part of the spinal cord.

Spinal Cord Anatomy

• Gray Matter: Contains neuronal cell bodies.

• White Matter: Consists of myelinated axons.

• Spinal Meninges: Includes pia, arachnoid, and dura mater.

• Regions:

  • Dorsal Horn: Contains sensory neurons.

  • Ventral Horn: Contains motor neurons.

  • Lateral Horn: Autonomic motor neurons.

• Dorsal Root Ganglion (DRG): Contains cell bodies of sensory neurons, facilitating sensation pathways to the CNS.

Reflexes

• Definition: Involuntary reaction to a peripheral stimulus.

• Reflex Arc: The simplest neural pathway responsible for receiving stimuli and generating a response.

Basic Components of a Reflex Arc

1. Sensory Receptor: Detects the stimulus.

2. Sensory Neuron: Carries the impulse towards the CNS.

3. Interneuron: Processes the information (not always present in simple reflexes).

4. Motor Neuron: Carries the impulse away from the CNS to the effector.

5. Effector Organ: Produces a response (e.g., muscle or gland).

Types of Reflexes

• Stretch Reflex:

  • Simplest reflex associated with muscle contraction in response to stretching. Example - Patellar reflex (knee jerk).

• Withdrawal Reflex:

  • Function: Remove a limb from a painful stimulus, also called the flexor reflex.

Spinal Nerves and Plexuses

• 31 pairs of spinal nerves relaying information between the brain and the body.

• Organized into major plexuses:

  • Cervical Plexus: Innervates neck and diaphragm.

  • Brachial Plexus: Controls upper limb function.

  • Lumbosacral Plexus: Innervates lower limb and pelvic region.

Dermatomes and Myotomes

• Dermatome: Area of skin supplied by a pair of spinal nerves; useful for assessing sensory functions.

• Myotome: Specific motor functions linked to nerve roots.

Cranial Nerves

• 12 pairs categorized as sensory or motor, with origins primarily in the brainstem.

Functions of Cranial Nerves

• CN I: Olfactory - Sense of smell.

• CN II: Optic - Vision.

• CN III: Oculomotor - Eye movement and pupil constriction.

• CN IV: Trochlear - Eye movement.

• CN V: Trigeminal - Sensory to face; motor to chewing muscles.

• CN VI: Abducens - Eye movement.

• CN VII: Facial - Expressions; taste; salivary glands.

• CN VIII: Vestibulocochlear - Hearing and balance.

• CN IX: Glossopharyngeal - Taste and swallowing; salivary glands.

• CN X: Vagus - Innervates thorax and abdomen organs.

• CN XI: Accessory - Neck movement muscles.

• CN XII: Hypoglossal - Tongue movement.

Autonomic Nervous System (ANS)

• Divided into Sympathetic and Parasympathetic components.

Differences in ANS Functions