BIOS EXAM 4

Chapter 15: Giant Multipolar Neuron

  • Function is key to understanding the following:

    • Major structures of the giant multipolar neuron:

      • Dendrites: Branching extensions that receive chemical signals (neurotransmitters) from other neurons and transmit them as electrical signals towards the cell body. They increase the surface area for synaptic contact.

      • Axons: A long, slender projection that conducts electrical impulses (action potentials) away from the neuron's cell body to transmit signals to other neurons, muscles, or glands. Axons are often myelinated to speed up impulse conduction.

      • Axon hillock: A specialized part of the cell body (soma) of a neuron that connects to the axon. It is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon. It is critical for initiating action potentials.

      • Nodes of Ranvier: Gaps in the myelin sheath along the axon. These gaps allow for the regeneration of the action potential via a process called saltatory conduction, which significantly increases the speed of nerve impulse transmission.

  • Important Note: Information may appear in questions but is not on the objective list.

Chapter 17: Gross Anatomy of the Brain and Cranial Nerves
Major Components

  • Review of brain anatomy includes:

    • Identification of major lobes of the brain:

      • Frontal lobe: Located at the front of the brain, associated with reasoning, planning, parts of speech, movement, emotions, and problem-solving.

      • Parietal lobe: Situated behind the frontal lobe, involved in processing sensory information such as touch, temperature, pain, and pressure. Also plays a role in spatial awareness and navigation.

      • Occipital lobe: Located at the rear of the brain, primarily responsible for visual processing.

      • Temporal lobe: Located beneath the frontal and parietal lobes, involved in processing auditory information, memory, and emotion.

      • Important Note: The insula is not required for the exam.

Functions of Major Brain Lobes

  • Frontal Lobe:

    • General Function: Motor control and higher-level cognitive functions.

    • Specific Function: Controls voluntary movement, executive functions like decision-making, planning, and personality.

  • Parietal Lobe:

    • General Function: Sensory information processing.

    • Specific Function: Somatosensory processing, including proprioception (awareness of body position), touch, pain, and temperature. Also involved in integrating sensory information and spatial manipulation.

  • Temporal Lobe:

    • General Function: Sensory (auditory) and memory processing.

    • Specific Function: Hearing, language comprehension (Wernicke's area), and formation of long-term memories.

  • Occipital Lobe:

    • General Function: Vision.

    • Specific Function: Processes visual information from the eyes, including color, form, and motion perception.

  • Central Sulcus:

    • Function: A prominent fissure that divides the frontal lobe from the parietal lobe. It also separates the primary motor cortex (precentral gyrus) from the primary somatosensory cortex (postcentral gyrus).

Gyri Associated with the Lobes

  • Precentral Gyrus:

    • Location: Frontal lobe, anterior to the central sulcus.

    • Function: Serves as the primary motor cortex, initiating voluntary movements.

  • Postcentral Gyrus:

    • Location: Parietal lobe, posterior to the central sulcus.

    • Function: Serves as the primary somatosensory cortex, receiving main sensory information from the body (e.g., touch, temperature, pain, proprioception).

Mid Sagittal Brain Structures (Relevant to Page 274)

  • Key Structures:

    • Pons: Part of the brainstem, acts as a bridge for nerve fibers connecting the cerebrum and cerebellum. Involved in sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.

    • Medulla Oblongata: Located at the base of the brainstem, controlling autonomic functions like breathing, heart rate, and blood pressure. Also involved in reflexes such as vomiting, coughing, and sneezing.

    • Midbrain: The uppermost part of the brainstem, involved in motor movement, particularly movements of the eye, and in auditory and visual processing.

    • Thalamus: A large, dual-lobed mass of gray matter located deep within the brain, acting as a relay station for all sensory information (except smell) to the cerebral cortex. Crucial for consciousness, sleep, and alertness.

    • Hypothalamus: Located below the thalamus, it controls the autonomic nervous system and regulates body temperature, hunger, thirst, sleep, and various aspects of metabolism and emotion.

    • Cerebellum: Located at the back of the brain, primarily responsible for coordinating voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity.

  • Potential exam queries may include asking for functions of specific structures such as the medulla.

Meninges (Page 277)

  • Three layers of the meninges (protective membranes surrounding the brain and spinal cord):

    • Dura Mater: The outermost, thickest, and toughest layer. It is a protective sac, often described as leathery.

    • Arachnoid Mater: The middle layer, named for its spiderweb-like appearance. It contains the subarachnoid space filled with cerebrospinal fluid (CSF).

    • Pia Mater: The innermost, delicate layer that adheres directly to the surface of the brain and spinal cord, following all their contours.

  • Identifying one of these layers is essential.

  • Superior Sagittal Sinus:

    • Description: A large, flat, wide venous channel (referred to as a sinus) located within the dura mater along the midline of the brain. It collects deoxygenated blood and CSF from the brain and drains it into the internal jugular veins.

Cranial Ventricles and Nerves (Pages 280-282)

  • Ventricular Structures (a system of interconnected cavities within the brain that produce and circulate cerebrospinal fluid):

    • Lateral Ventricles: Two C-shaped cavities, one in each cerebral hemisphere, connected to the third ventricle.

    • Third Ventricle: A narrow, median cavity located between the two halves of the thalamus. Its head resembles a gargoyle due to its shape.

    • Fourth Ventricle: Located between the pons and cerebellum, connecting to the central canal of the spinal cord. It is the wide part of the tail in anatomical representations.

  • Identifying cranial nerves and their functions is expected. There are 12 pairs of cranial nerves that emerge directly from the brain:

    • Example cranial nerves:

      • Oculomotor Nerve (III): Primarily controls most eye movements, including eyelid elevation and pupil constriction.

      • Olfactory Nerve (I): Responsible for the sense of smell.

      • Optic Nerve (II): Transmits visual information from the retina to the brain.

      • Other important nerves include: Trigeminal (V - facial sensation and mastication), Facial (VII - facial expression and taste), Vestibulocochlear (VIII - hearing and balance), Vagus (X - parasympathetic control of heart, lungs, and digestive tract).

    • Exam questions may ask for: "Give me the name and the function?"

Cranial Nerve Functionality Mnemonic

  • Mnemonic for remembering nerve types (Sensory, Motor, or Both):

    • "Some say marry money, but my brother says big boobs matter more."

    • Each starting letter corresponds to a cranial nerve from I to XII: S (Sensory), M (Motor), B (Both).

      • I: Olfactory (S)

      • II: Optic (S)

      • III: Oculomotor (M)

      • IV: Trochlear (M)

      • V: Trigeminal (B)

      • VI: Abducens (M)

      • VII: Facial (B)

      • VIII: Vestibulocochlear (S)

      • IX: Glossopharyngeal (B)

      • X: Vagus (B)

      • XI: Accessory (M)

      • XII: Hypoglossal (M)

    • Differentiates sensory, motor, and both sensory and motor functions for each of the 1212 cranial nerves.

Brainstem Structures

  • Midbrain features:

    • Corpora Quadrigemina: Four prominent swellings on the posterior aspect of the midbrain.

      • Superior Colliculus: Two upper bumps, primarily involved in visual reflex activities, such as tracking moving objects and reflexively turning the head in response to visual stimuli.

      • Inferior Colliculus: Two lower bumps, primarily involved in auditory reflex activities, such as the startle reflex to sudden loud noises and relaying auditory information to the thalamus.

    • These are noted as prominent bumps on the brain stem.

Spinal Cord Anatomy

  • Key Features:

    • Gray Matter: H-shaped region in the center of the spinal cord, consisting primarily of neuron cell bodies, dendrites, and unmyelinated axons. It is involved in processing information.

    • White Matter: Surrounds the gray matter, composed of myelinated axons organized into tracts. These tracts carry ascending (sensory) and descending (motor) information between the brain and the body.

    • Central Canal: A cerebrospinal fluid-filled channel that runs down the center of the spinal cord, continuous with the ventricles of the brain.

    • Gray Commissure: A bridge of gray matter that connects the two halves of the gray matter allowing communication between them.

    • Understanding the peripheral nerves involved:

      • Dorsal Root Ganglion: A cluster of nerve cell bodies (ganglion) located on the posterior (dorsal) root of a spinal nerve. It contains the cell bodies of sensory neurons.

      • Dorsal Root: The nerve root that emerges from the spinal cord containing only afferent (sensory) nerve fibers, transmitting sensory information from the body to the spinal cord.

Nerve Innervation Overview (Page 308)

  • Nerves innervating the arm (from the brachial plexus) include:

    • Axillary Nerve: Innervates the deltoid and teres minor muscles, important for shoulder abduction and rotation.

    • Musculocutaneous Nerve: Innervates the biceps brachii, brachialis, and coracobrachialis muscles (flexors of the arm and forearm).

    • Radial Nerve: Innervates the triceps brachii and all extensors of the forearm and hand. Crucial for wrist and finger extension.

    • Ulnar Nerve: Innervates most intrinsic hand muscles and some forearm flexors. Essential for fine motor control of the hand and sensation to the medial hand.

    • Median Nerve: Innervates most flexors of the forearm and hand, and muscles of the thumb. Important for movements of the thumb, wrist, and fingers.

  • Note on leg innervation:

    • Pudendal Nerve: Primary nerve of the perineum, responsible for sensation and motor function of the perineal region, external genitalia, and sphincter control.

    • Sciatic Nerve: The longest and widest nerve in the human body, originating in the lower back and extending down the back of the leg. It innervates many posterior thigh muscles and splits into:

      • Common Fibular Nerve (also known as common peroneal nerve): Branches into superficial and deep fibular nerves, innervating muscles for ankle dorsiflexion and foot eversion.

      • Tibial Nerve: Innervates muscles of the posterior lower leg and foot, crucial for ankle plantarflexion and toe flexion.