Key Takeaways
- The nervous system is divided into the CNS (brain and spinal cord) and PNS (cranial and spinal nerves)
- Neurons transmit signals: dendrites receive, cell body processes, axon transmits, synaptic terminal releases neurotransmitters
- The brain has four major regions: cerebrum (thinking), cerebellum (coordination), brainstem (vital functions), diencephalon (relay/hormones)
- The PNS includes the somatic (voluntary) and autonomic (involuntary) divisions; autonomic divides into sympathetic ("fight or flight") and parasympathetic ("rest and digest")
- The endocrine system uses hormones (chemical messengers) secreted by glands into the bloodstream for slow, long-lasting effects
- The hypothalamus links the nervous and endocrine systems; the pituitary gland is the "master gland"
- Key hormones: insulin (lowers blood sugar), glucagon (raises blood sugar), thyroid hormones (metabolism), cortisol (stress response)
- Negative feedback: most hormone levels are regulated by negative feedback (e.g., high thyroid hormone inhibits TSH release)
Nervous & Endocrine Systems
The nervous and endocrine systems are the body's two communication systems. The nervous system provides rapid, precise signaling, while the endocrine system provides slower, widespread hormonal regulation.
Nervous System Organization
| Division | Components | Function |
|---|---|---|
| Central Nervous System (CNS) | Brain and spinal cord | Processing center; integration and coordination |
| Peripheral Nervous System (PNS) | 12 cranial nerves, 31 spinal nerves | Connects CNS to the rest of the body |
PNS Subdivisions
| Division | Function | Control |
|---|---|---|
| Somatic | Controls skeletal muscles | Voluntary |
| Autonomic | Controls organs, glands, smooth muscle | Involuntary |
The autonomic nervous system has two branches:
| Branch | Nickname | Function | Effects |
|---|---|---|---|
| Sympathetic | "Fight or flight" | Prepares body for stress/danger | Increased heart rate, dilated pupils, bronchodilation, decreased digestion |
| Parasympathetic | "Rest and digest" | Promotes calming functions | Decreased heart rate, constricted pupils, bronchoconstriction, increased digestion |
Neurons
Neurons are the functional cells of the nervous system:
| Part | Function |
|---|---|
| Dendrites | Receive incoming signals from other neurons |
| Cell body (soma) | Contains the nucleus; processes signals |
| Axon | Long projection that carries signals away from the cell body |
| Myelin sheath | Insulating layer that speeds signal transmission |
| Synaptic terminal | End of the axon; releases neurotransmitters |
| Synapse | Gap between neurons where neurotransmitters cross |
Signal transmission: Electrical signal travels along the neuron → reaches the synaptic terminal → releases neurotransmitters into the synapse → neurotransmitters bind to the next neuron's receptors
The Brain
| Region | Function |
|---|---|
| Cerebrum | Higher functions: thinking, memory, speech, voluntary movement, sensory processing |
| Cerebellum | Coordination, balance, fine motor control |
| Brainstem | Vital functions: breathing, heart rate, blood pressure, consciousness |
| Diencephalon (thalamus/hypothalamus) | Thalamus: sensory relay; Hypothalamus: homeostasis, hormones, temperature |
The cerebrum is divided into four lobes:
| Lobe | Location | Function |
|---|---|---|
| Frontal | Front | Reasoning, planning, voluntary movement, speech production (Broca's area) |
| Parietal | Top/middle | Sensory processing (touch, temperature, pain), spatial awareness |
| Temporal | Sides | Hearing, memory, speech comprehension (Wernicke's area) |
| Occipital | Back | Vision |
Endocrine System
The endocrine system consists of glands that secrete hormones directly into the bloodstream:
| Gland | Key Hormones | Function |
|---|---|---|
| Hypothalamus | Releasing/inhibiting hormones | Links nervous and endocrine systems; controls pituitary |
| Pituitary (anterior) | GH, TSH, ACTH, FSH, LH, prolactin | "Master gland" — controls other glands |
| Pituitary (posterior) | ADH, oxytocin | Water balance, labor contractions, milk ejection |
| Thyroid | T3, T4, calcitonin | Metabolism, calcium regulation (lowers) |
| Parathyroid | PTH | Calcium regulation (raises blood calcium) |
| Adrenal cortex | Cortisol, aldosterone | Stress response, electrolyte balance |
| Adrenal medulla | Epinephrine, norepinephrine | Fight-or-flight response |
| Pancreas | Insulin, glucagon | Blood sugar regulation |
| Ovaries | Estrogen, progesterone | Female reproductive development |
| Testes | Testosterone | Male reproductive development |
Blood Sugar Regulation
| Hormone | Gland | Action | Released When |
|---|---|---|---|
| Insulin | Pancreas (beta cells) | Lowers blood sugar (stores glucose in cells) | Blood sugar is HIGH |
| Glucagon | Pancreas (alpha cells) | Raises blood sugar (releases glucose from liver) | Blood sugar is LOW |
Diabetes mellitus results from insufficient insulin production (Type 1) or insulin resistance (Type 2).
Hormone Regulation: Negative Feedback
Most hormones are regulated by negative feedback loops:
Example — Thyroid hormones:
- Hypothalamus releases TRH → stimulates pituitary
- Pituitary releases TSH → stimulates thyroid
- Thyroid releases T3/T4 → increases metabolism
- High T3/T4 → inhibits hypothalamus and pituitary → less TRH and TSH
- T3/T4 levels decrease → cycle restarts
The sympathetic nervous system is often called the:
Which hormone LOWERS blood sugar levels?
Which lobe of the cerebrum is responsible for vision?
Match each endocrine gland to its primary hormone(s).
Match each item on the left with the correct item on the right
The _____ is the part of the neuron that receives incoming signals from other neurons.
Type your answer below
The hypothalamus is critical because it: