Human nervous system

What are two main components of the central nervous system?

• The brain controls thinking, emotions, decision-making, and involuntary functions

• The spinal cord connects the brain to the body and controls reflexes.

Name the four lobes of the cerebreal cortex. What is a primary function associated with each lobe?

• Frontal lobe: Responsible for executive functions like planning, decision-making, personality, and voluntary motor control.

• Parietal lobe: Processes touch, pressure, temperature, and spatial awareness through the somatosensory cortex.

• Temporal lobe: Handles auditory processing, language comprehension (Wernicke’s area), and memory.

• Occipital lobe: Processes visual input from the eyes, including shape, color, and motion.

What are the three main parts of the brainstem, listed from superior to inferior?

1. Midbrain (top): Visual and auditory reflexes, motor movement, alertness

2. Pons (middle): Relays messages between cerebrum and cerebellum; involved in breathing,sleep regulation, facial expressions, and posture

3. Medulla oblongata (bottom): Controls vital autonomic functions like heart rate, breathing, digestion, blood pressure

Describe the role of the thalamus in sensory processing. What other brain region is it closely associated with functionally?

• The thalamus acts as a sensory relay station, processing all sensory input except smell.

• It sends information to the correct areas of the cerebral cortex for interpretation.

• It works closely with the cerebral cortex.

What is the primary function of the cerebellum? Explain why damage to the cerebellum might result in difficulty with fine motor movements.

The primary function of the cerebellum is to coordinate voluntary movements and ensure they are smooth, balanced, and precise. It also plays a key role in:

• Maintaining posture and balance

• Controlling muscle tone

• Fine-tuning motor activity based on feedback from the body and cerebral cortex

• Motor learning, like learning to ride a bike or play an instrument

If the cerebellum is damaged, this coordination breaks down—leading to poor balance, clumsy movements, and difficulty with tasks like writing, buttoning a shirt, or walking smoothly. That’s because the brain can still send movement commands, but without the cerebellum’s fine-tuning, those movements become uncoordinated.

What is the corpus callosum and what is its main function?

The corpus callosum is a thick band of nerve fibers that connects the left and right cerebral hemispheres of the brain.

Main Function: Its primary role is to enable communication between the two hemispheres.

This allows:

• Integration of sensory, motor, and cognitive information from both sides of the body

• Coordination of complex tasks that require input from both hemispheres (e.g., language processing, spatial reasoning, motor control)

Explain the concept of decussation in the central nervous system. Provide one example of a pathway that exhibits decussation.

Decussation in the central nervous system refers to the crossing over of nerve fibers from one side of the body to the opposite side of the brain or spinal cord. This explains why the left side of the brain controls the right side of the body, and vice versa.

+Because of decussation, damage to one side of the brain often affects the opposite side of the body. For example, a stroke in the left hemisphere may cause weakness or paralysis on the right side.

What are spinal nerves and where do they originate? What types of signals do they carry?

Spinal nerves are mixed nerves that connect the spinal cord to the body, enabling communication with the brain.

• 31 pairs emerge from the spinal cord at each vertebral level (cervical to coccygeal).

• Each nerve forms from two roots:

  • Dorsal root – carries sensory (afferent) input to the spinal cord

  • Ventral root – carries motor (efferent) output to muscles

They transmit both sensory and motor signals, linking the brain to the limbs, organs, and skin.

What is the autonomic nervous system? Briefly describe the two main divisions of the ANS and their general functions.

The autonomic nervous system (ANS) controls involuntary body functions, such as heart rate, digestion, and breathing.

It has two main divisions:

1. Sympathetic Nervous System – activates the “fight or flight” response (e.g. increases heart rate, dilates pupils, inhibits digestion).

2. Parasympathetic Nervous System – promotes “rest and digest” functions (e.g. slows heart rate, stimulates digestion, promotes energy storage).

Together, they maintain homeostasis by balancing activation and relaxation in body systems.

What is a neuron and what are its main parts?

A neuron is a nerve cell that sends and receives electrical signals in the nervous system. It’s the basic unit of communication in the brain, spinal cord, and nerves.

Main parts of a neuron:

1. Dendrites – Branch-like extensions that receive signals from other neurons.

2. Cell Body (Soma) – Contains the nucleus and processes incoming signals.

3. Axon – A long fiber that transmits signals away from the cell body to other neurons or muscles.

4. Axon Terminals – Endings that release neurotransmitters to pass the signal to the next cell.

5. Myelin Sheath – Fatty covering that insulates the axon and speeds up signal transmission.

What role does myelin play in nerve conduction?

+Myelin is a fatty insulating layer that wraps around axons and greatly increases the speed of electrical signal transmission

+It allows the action potential to jump between gaps in the myelin (nodes of Ranvier) in a process called saltotory conduction.

How does a neuron communicate with another neuron?

A neuron communicates with another neuron through a synapse, which is the small gap between the axon terminal of one neuron and the dendrite of the next.

1. An electrical impulse (action potential) travels down the axon.

2. When it reaches the axon terminal, it triggers the release of neurotransmitters (chemical messengers) into the synaptic gap.

3. These neurotransmitters bind to receptors on the receiving neuron’s dendrite.

4. This can either excite the next neuron (starting a new impulse) or inhibit it (preventing an impulse), depending on the type of neurotransmitter.

What is difference between excitatory and inhibitory neurotransmitters?

Excitatory neurotransmitters make the receiving neuron more likely to fire an action potential (send a signal), while inhibitory neurotransmitters make it less likely to fire.

Key Differences:

• Excitatory:

  • Cause depolarization of the neuron

  • Example: Glutamate

  • Result: Promotes activity in the nervous system

• Inhibitory:

  • Cause hyperpolarization of the neuron

  • Example: GABA (gamma-aminobutyric acid)

  • Result: Dampens or controls activity, preventing overstimulation

How does the brain interpret the strength of a stimulus?

1. Frequency of action potentials – A stronger stimulus causes a neuron to fire more frequently (higher firing rate).

2. Number of neurons activated – Stronger stimuli also activate more sensory neurons, sending more signals to the brain.

What is temporal summation?

Temporal summation is when multiple signals from a single neuron arrive at a postsynaptic neuron in rapid succession. If these signals come close enough together in time, they can add up (summate) and cause the postsynaptic neuron to reach the threshold and fire an action potential.

What is spatial summation?

Spatial summation occurs when multiple presynaptic neurons fire at the same time, each releasing neurotransmitters onto the same postsynaptic neuron. The combined effect of these signals can add up to reach the threshold and trigger an action potential.

How does synaptic transmission convert an electrical signal into a chemical one, and back again?

Synaptic transmission converts an electrical signal to a chemical signal—and then back—like this:

1. Electrical → Chemical:

   • An action potential (electrical signal) travels down the axon to the axon terminal.

   • This triggers calcium channels to open, allowing Ca²⁺ into the terminal.

   • Calcium causes synaptic vesicles to release neurotransmitters into the synaptic cleft.

2. Chemical → Electrical:

   • Neurotransmitters bind to receptors on the postsynaptic neuron’s membrane.

   • This opens ion channels, changing the electrical charge of the postsynaptic cell.

   • If the signal is strong enough, it triggers a new action potential—an electrical signal continues.