Nervous System: Neurons, Stimuli, and Impulses

• The nervous system gathers information from internal and external environments, processes it, and generates responses.
• A stimulus is environmental information that prompts a response in an organism.
• Impulses are electrical signals that transmit messages within the nervous system.

Neurons

• Neurons, or nerve cells, are responsible for transmitting impulses.
• Sensory neurons carry impulses from sensory organs to the central nervous system (CNS).
• Motor neurons carry impulses from the CNS to the peripheral nervous system (PNS).
• Interneurons process information and relay commands to other interneurons or motor neurons.

Nervous System Evolution

• Nerve nets consist of simple, interconnected neurons with limited specialization.
• Nerve cords involve interneurons clustered together, forming a ring that extends to appendages.
• Ganglia are structures where interneurons connect.
• Cephalization refers to the concentration of sensory neurons and interneurons in a "head" region.
• The brain is a specialized cerebral ganglia.
• Chordates possess a spinal cord, leading to a highly developed nervous system with interconnected interneurons, sensory neurons, and motor neurons.

Nervous System

• The central nervous system (CNS) processes information and generates responses, comprising the brain and spinal cord, housed within the skull and vertebral column.
• Sensations are perceived in specific brain regions, and commands to muscles originate from specific areas as well.
• The spinal cord connects the brain to the rest of the body.
• The peripheral nervous system (PNS) carries responses to muscles, glands, and other tissues.
• The sensory division of the PNS consists of receptor cells that gather information and sensory neurons that transmit impulses to the CNS.
• The motor division of the PNS transmits impulses from the CNS to muscles and glands.

PNS

• The somatic nervous system regulates skeletal muscle movement and reflexes.
• A reflex is a rapid, automatic response generated by impulses that do not need to travel to the brain.
• The autonomic nervous system regulates involuntary activities, such as heart rate and sweat gland stimulation.
• The sympathetic nervous system prepares the body for intense activity, triggering the "fight or flight" response.
• The parasympathetic nervous system promotes rest and digestion.

Cerebrum

• The cerebrum receives and interprets sensory information and determines appropriate responses.
• The cerebrum is involved in learning, memory, and conscious thought.

Lobes

• The frontal lobe aids in thinking, planning, organizing, problem-solving, and short-term memory.
• The parietal lobe helps interpret sensory information like texture and temperature.
• The temporal lobe processes information from smell, taste, and sound, and is involved in memory storage.
• The occipital lobe processes visual information and connects it to stored memories.

Cerebellum

• The cerebellum coordinates movement and controls balance for activities like walking and standing.

Pons

• The pons connects the cerebrum and cerebellum.
• The pons relays sensory information to the cerebellum and thalamus.
• The pons contains subconscious somatic and visceral motor centers.
• The pons regulates the body's level of alertness upon waking.
• The pons manages pain signals.

Medulla Oblongata

• The medulla oblongata relays sensory information to the thalamus and brain stem.
• It contains autonomic centers that regulate vital signals and digestive system activities.
• It controls the functioning of many internal organs.
• Optic lobes are involved in vision.
• Olfactory bulbs are involved in the sense of smell.

Meninges

• Meninges are composed of 3 layers of membranes that protect the brain and spinal cord.
• The pia mater is the inner layer.
• The arachnoid is a web-like structure filled with fluid that cushions the brain.
• The dura mater is the tough outer layer.

Spinal Cord

• The vertebral column protects the spinal cord.
• Intervertebral discs between vertebrae contain a gelatinous substance called the nucleus pulposus, which cushions the spinal column.
• Throughout the day, these discs become compressed.
• With age, the loss of muscle strength contributes to spine curvature.