Nervous, Sensory, and Locomotor Systems

Question 1

Neurons

Answer 1

A specialized cell in the nervous system responsible for transmitting information throughout the body. Neurons consist of three main parts:

Cell Body (Soma): Contains the nucleus and organelles, maintaining the cell’s functions.
Dendrites: Branch-like structures that receive signals from other neurons and conduct these impulses toward the cell body.

Axon: A long, thin projection that transmits signals away from the cell body to other neurons, muscles, or glands. All the branches end with a synaptic end which relays signals to a receiving cell.
The axon may be covered with a myelin sheath, which speeds up signal transmission.

Neurons communicate through electrical impulses (action potentials) and chemical signals (neurotransmitters) at synapses, enabling complex processes like thought, sensation, movement, and regulation of bodily functions.

Question 2

Central Nervous System (CNS)

Answer 2

The part of the nervous system consisting of the brain and spinal cord. It processes and integrates sensory information, makes decisions, and coordinates motor output.

Brain: The control center for the body, responsible for thoughts, memory, emotions, and regulating bodily functions.
Spinal Cord: A conduit for signals between the brain and the rest of the body; also manages reflexes.
The CNS uses interneurons to process information, facilitating communication between sensory neurons (which bring input from the body) and motor neurons (which send commands to muscles and glands).

Question 3

Peripheral Nervous System (PNS)

Answer 3

The part of the nervous system outside the brain and spinal cord, consisting of nerves that connect the CNS to the rest of the body. It is divided into sensory (afferent) and motor (efferent) divisions.

Sensory Division: Transmits sensory input from receptors (e.g., skin, eyes) to the CNS via sensory neurons.
Motor Division: Carries motor commands from the CNS to muscles and glands via motor neurons.
The PNS facilitates the reflex arc, a rapid response mechanism where sensory neurons communicate with interneurons in the spinal cord, which immediately relay signals to motor neurons for quick actions.

Question 4

Sensory input

Answer 4

The process of gathering information from sensory receptors (e.g., eyes, ears, skin) about the external and internal environment. This information is then transmitted to the central nervous system (CNS) via sensory neurons.

Question 5

Intergration

Answer 5

The process by which the central nervous system (CNS) processes and interprets sensory input, combining it with existing knowledge and past experiences to make decisions and generate appropriate responses. This function is primarily carried out by interneurons in the brain and spinal cord. Integration allows for complex functions such as perception, reasoning, and coordination of motor output.

Question 6

Motor output

Answer 6

The response generated by the central nervous system (CNS) after processing sensory input. It involves sending signals through motor neurons to muscles or glands to produce an action or response, such as moving a limb, secreting hormones, or adjusting heart rate.

Question 7

Resting potential

Answer 7

Electrical charge difference across the membrane of a resting neuron.
Negative charge inside the neuron is maintained by the uneven distribution of ions, particularly (Na+) and (K+), through the actions of the sodium-potassium pump and ion channels. The resting potential represents the polarized state of the neuron, with the inside being negatively charged relative to the outside. This stable state is crucial for the neuron’s ability to generate and transmit action potentials, enabling neural communication and proper functioning of the nervous system.

Question 8

Action potential

Answer 8

A rapid change in the membrane potential of a neuron.
It occurs when a stimulus depolarizes the neuron’s membrane, causing voltage-gated sodium channels to open and allowing sodium ions to rush into the cell, reversing the charge.
This depolarization phase is followed by repolarization, where potassium channels open, allowing potassium ions to leave the cell, restoring the negative charge.
The resulting electrical impulse propagates along the neuron’s axon, enabling communication between neurons and transmission of signals throughout the nervous system.

Question 9

Propagation of the signal

Answer 9

The transmission of an action potential along the axon of a neuron.

Depolarization: At the start of the action potential, voltage-gated sodium channels open, allowing sodium ions to rush into the neuron, depolarizing the membrane.

Repolarization: Potassium channels open, allowing potassium ions to leave the neuron, restoring the negative charge inside the cell and repolarizing the membrane.

Propagation: The depolarization at one point of the neuron triggers voltage-gated sodium channels to open in adjacent regions of the membrane, initiating a new action potential. This process continues down the length of the axon, allowing the signal to travel quickly and efficiently.

Propagation ensures that the signal travels unidirectionally from the dendrites, through the cell body, and down the axon to the axon terminals, facilitating communication between neurons and transmission of information throughout the nervous system.

Question 10

Chemical synapses

Answer 10

Specialized junctions between neurons where communication occurs via chemical signals called neurotransmitters. When an action potential reaches the presynaptic neuron’s axon terminal, it triggers the release of neurotransmitters into the synaptic cleft. These neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic neuron, leading to changes in its membrane potential and potentially generating a new action potential. Chemical synapses allow for precise control and modulation of neuronal signaling, playing a fundamental role in information processing and transmission within the nervous system.

Question 11

Cerebrospinal fluid

Answer 11

Clear fluid surrounding the brain and spinal cord, providing cushioning, chemical stability, and waste removal. Produced in the brain’s ventricles, it flows through the subarachnoid space and is reabsorbed into the bloodstream.

Question 12

Meninges

Answer 12

Protective layers surrounding the brain and spinal cord, consisting of the dura mater, arachnoid mater, and pia mater. They provide physical support, cushioning, and stability to the central nervous system.

Question 13

Motor system

Answer 13

The motor system encompasses the motor cortex in the brain, initiating and coordinating voluntary movements. Signals from the motor cortex travel via motor neurons in the spinal cord and peripheral nervous system to muscles and glands, executing actions.

Question 14

Autonomic Nervous System (ANS)

Answer 14

Regulates involuntary bodily functions, maintaining internal homeostasis. It comprises sympathetic and parasympathetic divisions:

Sympathetic Division: Activates “fight or flight” responses, increasing heart rate, dilating pupils, and mobilizing energy reserves to prepare the body for action in stressful situations.

Parasympathetic Division: Opposes sympathetic activity, promoting “rest and digest” functions. It slows heart rate, constricts pupils, and enhances digestion and relaxation to conserve energy and restore balance after stress.

The ANS functions autonomously, controlling vital processes such as heart rate, respiration, digestion, and glandular activity, without conscious effort.

Question 15

Brainstem

Answer 15

A vital part of the central nervous system located at the base of the brain, connecting the cerebrum with the spinal cord. It consists of three main structures:

Medulla Oblongata: Controls vital functions such as heartbeat, breathing, blood pressure, and reflexes like swallowing and vomiting.

Pons: Acts as a bridge between different parts of the brain, facilitating communication. It also regulates breathing and plays a role in sleep and arousal.

Midbrain: Coordinates sensory and motor functions, serving as a relay center for auditory and visual reflexes.

The brainstem regulates fundamental bodily functions, relays sensory and motor signals, and plays a crucial role in maintaining consciousness and overall homeostasis.

Question 16

Cerebellum

Answer 16

A highly folded structure located at the base of the brain, beneath the cerebrum, comprising two hemispheres. The cerebellum is primarily responsible for coordinating voluntary movements, balance, and posture. It receives input from sensory systems and the cerebral cortex, allowing it to fine-tune motor activities and ensure smooth, coordinated movements. Additionally, the cerebellum plays a role in motor learning and cognitive functions such as attention and language processing.

Question 17

Cerebrum

Answer 17

The largest part of the brain, occupying most of the cranial cavity, and divided into left and right hemispheres. It is responsible for higher brain functions, including cognition, sensory perception, motor control, and emotional processing. The cerebrum is divided into lobes—frontal, parietal, temporal, and occipital—each with specific roles in processing different types of information. It contains the cerebral cortex, which is highly convoluted to increase surface area and accommodate billions of neurons. The cerebrum integrates sensory information, initiates voluntary movements, and supports complex cognitive functions such as memory, language, and problem-solving.

Question 18

Hypothalamus

Answer 18

A small region located below the thalamus at the base of the brain, forming a critical link between the nervous system and the endocrine system. The hypothalamus plays a central role in regulating homeostasis by controlling various bodily functions, including body temperature, hunger, thirst, sleep-wake cycles, and circadian rhythms. It also regulates the release of hormones from the pituitary gland, serving as a master regulator of the endocrine system. Additionally, the hypothalamus is involved in emotional responses and certain behaviors, such as aggression and sexual behavior.

Question 19

Converting a Stimulus to an Electrical Signal

Answer 19

Also known as sensory transduction, this process involves the conversion of a physical or chemical stimulus into an electrical signal by sensory receptors.

Detection: Sensory receptors (e.g., photoreceptors in the eyes, mechanoreceptors in the skin) detect a specific type of stimulus (light, pressure, etc.).

Transduction: The stimulus causes ion channels in the receptor cell membrane to open or close, leading to a change in the cell’s membrane potential.

Generation of Electrical Signal: If the change in membrane potential reaches a threshold, it triggers an action potential in the sensory neuron, converting the initial stimulus into an electrical signal.

Transmission: The action potential travels along the sensory neuron to the central nervous system, where it is processed and interpreted.

This process allows the body to perceive and respond to various environmental stimuli.

Question 20

Pain receptors

Answer 20

Sensory receptors that detect harmful stimuli, such as mechanical damage, extreme temperatures, and chemicals from injured tissues, causing the perception of pain.

Activation: Harmful stimuli trigger nociceptors, generating an electrical signal.

Transmission: The signal travels to the spinal cord and brain.
Perception: The brain processes the signals, resulting in pain awareness.

Pain receptors help protect the body by signaling potential harm.

Question 21

Thermoreceptors

Answer 21

Sensory receptors that detect changes in temperature. They are found in the skin, body core, and hypothalamus.

Cold Receptors: Activated by cooling temperatures.
Heat Receptors: Activated by warming temperatures.
Thermoreceptors help regulate body temperature by sending signals to the brain to initiate appropriate responses, such as sweating or shivering.

Question 22

Mechanoreceptors

Answer 22

Sensory receptors that detect mechanical stimuli such as pressure, touch, vibration, and stretch. They are found in the skin, muscles, joints, and internal organs.

Types: Includes receptors for light touch (Meissner’s corpuscles), deep pressure (Pacinian corpuscles), and stretch (muscle spindles).

Function: Convert mechanical forces into electrical signals (action potentials) that are transmitted to the brain, allowing perception of physical sensations.

Mechanoreceptors enable the body to respond to mechanical changes in the environment, playing a crucial role in tactile sensation, proprioception, and balance.

Question 23

Chemoreceptors

Answer 23

Sensory receptors that detect chemical stimuli in the environment or body fluids. They are found in the taste buds, nasal cavity, and various internal organs.

Taste Receptors: Detect chemicals in food and drink.
Olfactory Receptors: Detect airborne chemicals (smell).
Internal Chemoreceptors: Monitor changes in blood chemistry, such as oxygen, carbon dioxide, and pH levels.
Chemoreceptors convert chemical signals into electrical signals, allowing the brain to process taste, smell, and internal chemical states, contributing to homeostasis and sensory perception.

Question 24

Electromagnetic receptors

Answer 24

Sensory receptors that detect electromagnetic energy such as light, electricity, and magnetism.

Photoreceptors: Found in the retina of the eyes; detect light and are responsible for vision.
Electroreceptors: Found in some aquatic animals; detect electrical fields in the environment.
Magnetoreceptors: Found in certain animals; detect magnetic fields and aid in navigation.
These receptors convert electromagnetic stimuli into electrical signals, enabling organisms to perceive and respond to their environment.

Question 25

Lighting the retina

Answer 25

The process by which light is focused onto the retina, the light-sensitive layer at the back of the eye, enabling vision.

Light Entry: Light enters the eye through the cornea and passes through the pupil, which is regulated by the iris (the colored part of the eye that controls the size of the pupil).

Focusing: The lens adjusts its shape to focus light onto the retina.

Photoreception: Photoreceptors (rods and cones) in the retina detect light and convert it into electrical signals.

Signal Transmission: Electrical signals are transmitted to the brain via the optic nerve, where they are processed into visual images.
This process allows the eye to detect and interpret light, enabling sight.

Question 26

Rods

Answer 26

Photoreceptor cells in the retina of the eye that are sensitive to low levels of light, enabling vision in dim or dark conditions.

Function: Specialized for night vision (scotopic vision) and peripheral vision.

Structure: Long and cylindrical with a single type of light-sensitive pigment (rhodopsin).

Sensitivity: Highly sensitive to light, allowing detection of low-intensity light but providing limited color vision and visual acuity.

Location: Predominantly found in the peripheral regions of the retina.

Role: Provide black-and-white vision in low-light conditions and contribute to the detection of motion and shapes in dim environments.

Question 27

Cones

Answer 27

Photoreceptor cells in the retina of the eye that are responsible for color vision and high visual acuity in bright light conditions.

Function: Specialized for daylight vision (photopic vision) and color discrimination.

Structure: Shorter and tapered compared to rods, with three types of light-sensitive pigments (red, green, and blue cones) responsible for color vision.

Sensitivity: Less sensitive to light compared to rods, requiring higher light levels for activation.

Color Vision: Enable discrimination of colors by responding to different wavelengths of light, allowing perception of a wide range of hues.

Location: Concentrated in the fovea, the central region of the retina, which is responsible for high-resolution vision.

Question 28

Nearsightedness

Answer 28

Nearsighted people cannot focus on well on distant objects, although they can see well at short distances. A near sighted eyeball is longer than normal, and it focuses distant objects in front of the retina instead of on it. Corrected by lenses that are thinner towards the middle.

Question 29

Farsightedness

Answer 29

Farsightedness occurs when the eyeball is shorter than normal, causing the lens to focus images behind the retina. Corrected by lenses that are thicker towards the middle.

Question 30

Astigmatism

Answer 30

Blurred vision caused by damaged cornea or lens. The distorsion makes light rays converge unevenly and not focus at any one point on the retina.

Question 31

Hearing

Answer 31

The process by which sound waves are detected by the ear and converted into electrical signals that are interpreted by the brain.

1. Sound Waves: Enter the ear canal and cause the eardrum to vibrate.
2. Middle Ear: Vibrations are transferred to the ossicles (tiny bones: malleus, incus, and stapes) which amplify the sound.
3. Inner Ear: The stapes transmits vibrations to the cochlea, a fluid-filled structure lined with hair cells.
4. Hair Cells: Movement of the cochlea fluid causes hair cells to bend, generating electrical signals.
5. Signal Transmission: Electrical signals travel via the auditory nerve to the brain, where they are interpreted as sound.

This process enables the perception of sound, allowing for communication, music appreciation, and awareness of environmental noises.

Question 32

The skeletal system

Answer 32

The framework of bones and connective tissues that supports the body, protects internal organs, and enables movement.

Endoskeleton: An internal skeleton made up of bones and cartilage, providing structural support and facilitating growth.

Bones: Provide structure, protect organs, and store minerals (e.g., calcium, phosphorus).

Joints: Connect bones, allowing for movement and flexibility.

Cartilage: Provides cushioning at joints and supports structures like the nose and ears.

Ligaments: Tough, elastic tissues that connect bones to other bones at joints.

Tendons: Connect muscles to bones, enabling movement.

Bone Marrow: Produces blood cells (red and white blood cells, platelets) in the medullary cavities of bones.

The skeletal system is essential for movement, protection, support, mineral storage, and blood cell production.

Question 33

The muscular system

Answer 33

The system of muscles in the body that enables movement, maintains posture, and produces heat.

Muscles: Made up of muscle fibers that contract to produce movement.
Types of Muscles:

Skeletal Muscles: Attached to bones, responsible for voluntary movements.

Smooth Muscles: Found in walls of internal organs, responsible for involuntary movements.

Cardiac Muscle: Found in the heart, responsible for pumping blood.

Tendons: Connect muscles to bones, transmitting the force of muscle contraction.

Muscle Contraction: Involves the sliding filament theory, where actin and myosin filaments slide past each other to shorten muscle fibers.

Functions: Movement, posture maintenance, joint stability, and heat production through muscle contractions.

The muscular system works in coordination with the skeletal system to facilitate movement and support various bodily functions.

Question 34

The cellular basis of muscle contraction.

Answer 34

The process by which muscle fibers contract to produce movement, involving the interaction of actin and myosin filaments within the muscle cells.

Muscle Fiber Structure: Composed of myofibrils, which contain repeating units called sarcomeres.

Sarcomeres: The functional units of muscle contraction, made up of actin (thin) and myosin (thick) filaments.

Sliding Filament Theory: During contraction, myosin heads bind to actin filaments, pulling them inward and shortening the sarcomere. Thin filaments slide past its thick filaments.

Role of Calcium: Calcium ions released from the sarcoplasmic reticulum bind to troponin, causing a change in the tropomyosin complex that exposes binding sites on actin for myosin.

ATP Role: ATP binds to myosin, allowing it to detach from actin and re-cock for another contraction cycle.’

Neuromuscular Junction: Motor neurons release neurotransmitters (acetylcholine) at the neuromuscular junction, triggering an action potential in the muscle fiber that leads to contraction.

Muscle contraction is a highly regulated process that enables voluntary and involuntary movements in the body.

Question 35

The sliding filament model of muscle contraction

Answer 35

1. ATP binds to a myosin head which is then released from an actin filament.
2. The breakdown of ATP makes the myosin head gain energy and change into a high-energy position.
3. Myosin head attaches to an actinn binding site.
4. The myosin head bends back to its low-energy, pulling the thin filament toward the center of the sacromere.
5. The process repeats as long as ATP is available.