Nervous System Divisions

• The nervous system has three main functions: sensory input, integration, and motor output.

Divisions of the Nervous System

• The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).

Central vs. Peripheral Nervous System

• The central nervous system (CNS) consists of the brain and spinal cord.
• The peripheral nervous system (PNS) consists of all the nervous tissue outside the brain and spinal cord.

Afferent (Sensory) Division of the PNS

• The afferent division of the PNS carries sensory information from receptors to the CNS.

Somatic vs. Visceral Branches of the Afferent Division

• The somatic sensory branch conveys impulses from skin, skeletal muscles, and joints.
• The visceral sensory branch transmits impulses from visceral organs.

Efferent (Motor) Division of the PNS

• The efferent division of the PNS transmits impulses from the CNS to effector organs (muscles and glands).

Somatic Branch of the Efferent Nervous System

• The somatic branch controls skeletal muscles and is responsible for voluntary movements.

Parasympathetic vs. Sympathetic Branches

• The parasympathetic branch promotes "rest and digest" functions, conserving energy, while the sympathetic branch is involved in "fight or flight" responses, expending energy.
• Parasympathetic neurons have long preganglionic fibers and short postganglionic fibers; sympathetic neurons have short preganglionic fibers and long postganglionic fibers.

Parts of the Central Nervous System

• The central nervous system includes the brain and the spinal cord.

Protection of the Brain and Spinal Cord

• The brain is protected by the bones of the skull.
• The spinal cord is protected by the bones of the vertebral column.

Layers of the Meninges

• The three layers of the meninges are the dura mater (outermost), arachnoid mater (middle), and pia mater (innermost).

Structure of the Meninges

• The dura mater is a tough, fibrous outer layer.
• The arachnoid mater is a web-like middle layer with cerebrospinal fluid in the subarachnoid space.
• The pia mater is a delicate inner layer that adheres directly to the surface of the brain and spinal cord.

Cerebrospinal Fluid

• Cerebrospinal fluid (CSF) is a clear fluid that surrounds the brain and spinal cord.
• It is located in the subarachnoid space and ventricles of the brain.
• Its role is to cushion and protect the brain and spinal cord, transport nutrients, and remove waste.

Brain Parts and Functions

• Cerebrum: Higher-level cognitive functions such as reasoning and problem-solving.
• Cerebellum: Coordinates movement and balance.
• Basal ganglia: Involved in motor control, motor learning, executive functions and behaviors, and emotions.
• Corpus callosum: Connects the left and right hemispheres of the brain.
• Medulla oblongata: Controls vital functions such as heart rate, breathing, and blood pressure.
• Hypothalamus: Regulates body temperature, hunger, thirst, and the sleep-wake cycle.

Cerebral Cortex Structure

• The cerebral cortex is the outer layer of the cerebrum.
• It is highly convoluted (folded) to increase surface area, allowing for more complex processing.

Lobes of the Cerebrum

• Frontal lobe: Involved in planning, decision-making, and motor control.
• Parietal lobe: Processes sensory information.
• Temporal lobe: Involved in auditory processing and memory.
• Occipital lobe: Processes visual information.

Grey vs. White Matter in the Brain

• Grey matter consists of neuron cell bodies and dendrites.
• White matter consists of myelinated axons.

Meninges in the Spinal Cord

• The meninges in the spinal cord have a similar structure to those in the brain, but with some differences in the arrangement of the dura mater.

Spinal Cord Parts

• Dorsal root: Contains sensory neurons entering the spinal cord.
• Dorsal root ganglion: Contains the cell bodies of sensory neurons.
• Spinal nerve: A mixed nerve containing both sensory and motor fibers.
• White matter: Surrounds the grey matter and contains myelinated axons.
• Grey matter: Contains neuron cell bodies, dendrites, and interneurons.
• Sensory neuron: Carries sensory information from receptors to the spinal cord.
• Motor neuron: Carries motor commands from the spinal cord to effectors.
• Interneuron: Connects sensory and motor neurons within the spinal cord.
• Ventral root: Contains motor neurons exiting the spinal cord.

Structure of White and Grey Matter in the Spinal Cord

• White matter is organized into columns containing ascending (sensory) and descending (motor) tracts.
• Grey matter is organized into horns, with dorsal horns receiving sensory information and ventral horns containing motor neurons.

Sensory Receptors

• Sensory receptors are specialized structures that detect changes in the environment.

Thermoreceptors

• Thermoreceptors are found in the skin, hypothalamus, and other areas.

Thermoreceptor Response

• Thermoreceptors respond to changes in temperature, with separate receptors for hot and cold.

Osmoreceptors

• Osmoreceptors are found in the hypothalamus.

Osmoreceptor Response

• Osmoreceptors respond to changes in osmotic pressure, helping to regulate fluid balance.

Chemoreceptors

• Chemoreceptors are found in the blood vessels, brain, and taste buds.

Chemoreceptor Response

• Chemoreceptors respond to changes in chemical concentrations.

Touch Receptors

• Touch receptors are found in the skin.

Distinguishing Light and Deep Touches

• Different types of touch receptors respond to different levels of pressure, allowing the body to distinguish between light and deep touches.

Pain Receptors

• Pain receptors (nociceptors) are found throughout the body.

Pain Receptor Function

• Nociceptors respond to tissue damage or potentially damaging stimuli.
• They differ from other receptors in that they have a higher threshold for activation and can respond to a variety of stimuli (e.g., mechanical, thermal, chemical).

Neuron Parts

• Dendrites: Receive signals from other neurons.
• Cell body (soma): Contains the nucleus and other organelles.
• Axon: Transmits signals to other neurons or effectors.
• Myelin sheath: Insulates the axon and speeds up signal transmission.
• Schwann cells: Form the myelin sheath in the PNS.
• Nodes of Ranvier: Gaps in the myelin sheath that allow for faster signal transmission.
• Axon terminal: Forms a synapse with another neuron or effector.

Nerve Impulse Path

• A nerve impulse travels from the dendrites to the cell body, down the axon, and to the axon terminals.

Structural Types of Neurons

• Multipolar neurons: Have many dendrites and one axon.
• Unipolar neurons: Have a single process that divides into two branches.
• Bipolar neurons: Have one dendrite and one axon.

Functional Types of Neurons

• Sensory neurons: Carry sensory information from receptors to the CNS.
• Interneurons: Connect sensory and motor neurons within the CNS.
• Motor neurons: Carry motor commands from the CNS to effectors.

Reflex Definition

• A reflex is a rapid, automatic response to a stimulus.

Properties of Reflexes

• Reflexes are involuntary, rapid, predictable, and stereotyped.

Reflex Arc

• The reflex arc includes a sensory receptor, sensory neuron, interneuron (in some cases), motor neuron, and effector.
• The nerve impulse travels from the sensory receptor along the sensory neuron to the spinal cord, where it may be processed by an interneuron before reaching the motor neuron, which carries the impulse to the effector.

Monosynaptic vs. Polysynaptic Reflexes

• Monosynaptic reflexes involve a direct connection between a sensory neuron and a motor neuron.
• Polysynaptic reflexes involve one or more interneurons between the sensory and motor neurons.

Examples of Reflexes

• Protective reflexes: Withdrawal reflex in response to pain.
• Acquired reflexes: Learned reflexes, such as those involved in driving.

Nerve Impulse

• A nerve impulse is an electrical signal that travels along a neuron.

Resting Membrane Potential

• Resting membrane potential is the electrical potential difference across the cell membrane of a neuron when it is not actively transmitting a signal.
• It is maintained by the sodium-potassium pump and the permeability of the membrane to ions.

Action Potential

• An action potential is a rapid, transient change in the membrane potential of a neuron that occurs when it is stimulated.

Phases of Action Potential

• Depolarization: The membrane potential becomes more positive due to the influx of sodium ions.
• Repolarization: The membrane potential returns to its resting value due to the efflux of potassium ions.
• Hyperpolarization: The membrane potential briefly becomes more negative than the resting potential.
• Recovery: The membrane potential returns to its resting value, and the ion gradients are restored.

Refractory Period

• The refractory period is a brief period after an action potential during which the neuron is less able to fire another action potential.

Nerve Impulse Transmission

• In an unmyelinated axon, the action potential travels continuously along the axon.
• In a myelinated axon, the action potential jumps from one node of Ranvier to the next, speeding up transmission (saltatory conduction).

Synapse

• A synapse is the junction between two neurons where communication occurs.

Nerve Impulse Transmission Across a Synapse

• When an action potential reaches the axon terminal, it triggers the release of neurotransmitters into the synaptic cleft.
• The neurotransmitters bind to receptors on the postsynaptic neuron, causing a change in its membrane potential and potentially triggering an action potential.