Grade 12 Life Sciences: The Human Nervous System

Flashcards covering the Grade 12 Life Sciences unit on the Human Nervous System, including CNS anatomy, brain structures, spinal cord, neurons, reflex arcs, synaptic transmission, neurological disorders, drug impacts, and sensory receptors.

Which two body systems act as major communication networks to coordinate bodily activities and maintain homeostasis?

The nervous system (using nerve impulses) and the endocrine system (using hormones).

What are the five primary functions of the vertebrate nervous system?

1) Gathering information via sense organs, 2) transmitting information to processing areas (brain and spinal cord), 3) processing information, 4) formulating a response to stimuli, and 5) sending impulses to effector organs (muscles and glands) to execute the response.

What are the three interactive subsystems that comprise the human nervous system?

The central nervous system (CNS / SSS), the peripheral nervous system (PNS / PSS), and the autonomic nervous system (ANS / OSS).

Based on the provided diagram, which structures comprise the central nervous system and which comprise the peripheral nervous system?

The central nervous system consists of the brain (brein) and spinal cord (rugmurg), while the peripheral nervous system consists of the cranial nerves (kraniale senuwees) and spinal nerves (spinale senuwees).

Name the three protective membranes (meninges) enclosing the brain and spinal cord, from outermost to innermost.

1) Dura mater (tough, fibrous outer membrane lining the skull), 2) Arachnoid membrane (aragnoïed; thin, vascular middle layer), and 3) Pia mater (delicate inner membrane lining the gyri of the brain).

Where is cerebrospinal fluid found, and what are its main functions?

It is located in the subarachnoid space (between the arachnoid and pia mater), the four brain ventricles, and the central canal of the spinal cord. It absorbs mechanical shock, maintains uniform pressure, and keeps nerve tissue moist.

What anatomical terms denote the folds and grooves on the surface of the cerebrum, and what is their functional purpose?

The folds are called gyri (girusse) and the grooves are called sulci (sulkusse); they increase the total surface area of the cerebral cortex.

What is the corpus callosum, and what is its primary function?

A thick band of white nerve fibers located beneath the cerebrum in the center of the brain that connects the left and right cerebral hemispheres, enabling communication between them.

What are the primary functional roles associated with each of the four cerebral lobes?

1) Frontal lobe: motor area controlling voluntary movement and speech; 2) Parietal lobe: interprets skin sensations; 3) Occipital lobe: visual processing center; 4) Temporal lobe: hearing, taste, and smell center.

How is grey matter and white matter distributed within the cerebrum?

The outer cortex is composed of grey matter (containing neuron cell bodies), whereas the inner medulla is composed of white matter (containing myelinated nerve fibers).

Describe the structural features of the cerebellum, including the vermis and arbor vitae.

The cerebellum consists of two hemispheres joined by a central band called the vermis, with shallow parallel surface gyri called folia. Its outer cortex is grey matter, and its inner medulla is white matter branching in a tree-like pattern known as the arbor vitae.

What are the primary functions of the cerebellum, and what condition results from its damage?

It coordinates voluntary skeletal muscle movements (ensuring smooth, controlled walking and running), maintains muscle tone, balance, posture, and equilibrium. Damage results in a lack of muscle coordination called ataxia (ataksie).

What homeostatic functions are regulated by the hypothalamus?

Control of body temperature, blood pressure, sleep cycles, appetite/hunger, thirst, and emotions.

What essential vital centers and reflex actions are housed in the medulla oblongata?

Essential centers include the respiratory center (breathing rate and depth), vasomotor center (blood pressure and temperature via vasodilation and vasoconstriction), and cardiomotor center (heart rate). Non-essential reflexes include salivation, coughing, blinking, hiccuping, and sneezing.

Why does the left cerebral hemisphere control the right side of the body and vice versa?

Nerve fibers cross over (decussate) from one side to the other within the medulla oblongata.

In the provided cross-sectional diagram of the spinal cord, identify the grey matter, white matter, and dorsal/ventral roots.

The inner butterfly/H-shaped zone is grey matter (with a central canal), surrounded externally by white matter. The upper root entering the back is the dorsal root, and the lower root exiting is the ventral root.

How do the dorsal and ventral roots of the spinal cord differ functionally?

The dorsal root carries sensory (afferent) impulses into the spinal cord from receptors and contains a ganglion, while the ventral root carries motor (efferent) impulses away from the spinal cord to effectors.

How many pairs of cranial and spinal nerves exist in the human peripheral nervous system?

There are $12$ pairs of cranial nerves and $31$ pairs of spinal nerves.

Compare the antagonistic functions of the sympathetic and parasympathetic nervous systems on heart rate, pupils, and peristalsis.

The sympathetic system accelerates heart rate, dilates pupils, and inhibits peristalsis (fight-or-flight), whereas the parasympathetic system slows heart rate, constricts pupils, and stimulates peristalsis (rest-and-digest).

What structural and functional difference distinguishes dendrites from an axon?

Dendrites conduct nerve impulses toward the cell body (soma), whereas an axon is typically a single, long extension that conducts nerve impulses away from the cell body toward synaptic terminals.

What cells produce the myelin sheath in the peripheral nervous system, and what is its role?

Schwann cells form the myelin sheath, which insulates the axon to prevent loss of electrical charge and accelerates the speed of nerve impulse transmission.

What are Nissl granules and where are they located?

Granules rich in RNA located within the cytoplasm of a neuron's cell body that participate in protein synthesis and cellular metabolism.

Identify the type of neuron shown in this diagram and state the direction in which it conducts impulses.

It is a motor (multipolar / efferent) neuron; it conducts nerve impulses away from the cell body along the axon toward effector organs (muscles or glands).

Identify the type of neuron shown in this diagram and describe its structural arrangement.

It is a sensory (unipolar / afferent) neuron; it has an off-center cell body (soma) located along the fiber with dendrites extending from receptors and an axon leading toward the central nervous system.

What is an interneuron (connector neuron) and where is it located?

A neuron situated entirely within the central nervous system (brain and spinal cord) that connects sensory neurons to motor neurons.

What is the difference between a reflex action and a reflex arc?

A reflex action is a rapid, automatic, involuntary response to a stimulus without conscious intervention by the brain, whereas a reflex arc is the specific neural pathway traversed by impulses during a reflex action.

Trace the step-by-step neural pathway of the reflex arc shown in the diagram.

Receptor (detects stimulus) $\rightarrow$ Sensory neuron (enters via dorsal root) $\rightarrow$ Interneuron (in grey matter of spinal cord) $\rightarrow$ Motor neuron (exits via ventral root) $\rightarrow$ Effector (muscle contracts).

What is a synapse, and what are its three primary biological functions?

A microscopic junction between the axon terminal of one neuron and the dendrite/membrane of another. It 1) ensures unidirectional impulse transmission, 2) prevents continuous overstimulation of neurons, and 3) mediates transmission from sensory to motor pathways.

How does chemical transmission occur across a synaptic cleft?

An incoming electrical impulse triggers synaptic vesicles to release neurotransmitters (e.g., acetylcholine) into the synaptic cleft. These diffuse across the gap, bind to receptors on the postsynaptic membrane to generate a new impulse, and are then degraded by specific enzymes.

What histological features characterize the brain tissue of a patient with Alzheimer's disease?

Loss of cortical neurons and synapses, presence of abnormal protein clumps called amyloid plaques (amiloïede plake), and neurofibrillary tangles (knope) of fiber bundles.

What is the underlying immunological cause of Multiple Sclerosis (MS)?

It is an autoimmune condition where helper T-cells recognize myelin antigens, destroying the myelin sheath around CNS nerve fibers and leaving behind patches of hardened scar tissue (plaques).

How do beta-interferons function in the therapeutic management of Multiple Sclerosis?

They slow the formation of scar tissue and reduce the frequency, duration, and severity of relapses, thereby slowing disease progression.

Differentiate between totipotent, pluripotent, and multipotent stem cells.

Totipotent cells (early embryo) can form any cell type including embryonic membranes; pluripotent cells (at approx. $5$ days) can differentiate into any body cell type except whole embryos; multipotent cells (adults) can only differentiate into limited cell types within specific organs.

How do depressant drugs and stimulant drugs differ in their effect on central neurotransmission?

Depressants enhance the inhibitory neurotransmitter GABA to reduce neuronal excitability, whereas stimulants elevate synaptic dopamine (increasing release and preventing reuptake) to overstimulate the CNS.

What is the psychoactive substance in cannabis (dagga), and which brain region does it disrupt to impair memory?

Tetrahydrocannabinol (THC); it activates cannabinoid receptors and disrupts sensory information processing in the hippocampus.

By how much can methamphetamine (tik) elevate dopamine levels compared to cocaine?

Cocaine raises dopamine concentrations to approximately $400\%$ of normal levels, whereas methamphetamine can surge dopamine up to $1500\%$.

What are the four primary receptor classes based on the nature of stimuli they detect?

1) Photoreceptors (light: rods and cones), 2) Chemoreceptors (chemicals: taste buds and olfactory cells), 3) Thermoreceptors (temperature: Ruffini and Krause endings), and 4) Mechanoreceptors (mechanical force: Pacinian and Meissner's corpuscles).

Differentiate between rods (stafies) and cones (keëltjies) in the human retina.

Rods perceive low light intensity and provide monochromatic (black and white) vision, whereas cones perceive color in bright light and are concentrated most densely in the fovea centralis.

Which cutaneous mechanoreceptors detect delicate touch versus deep pressure?

Meissner's corpuscles detect light touch, contact, and texture, while Pacinian corpuscles (Pacini-liggaampies) detect firm touch and deep pressure.

What is spasticity (spastisiteit) in the context of spinal cord injuries?

A condition characterized by sustained, involuntary muscle contractions resulting from damage to upper motor pathways or spinal cord tracts.