Neurons Hormones and the Brain Chapter 4 Neurons

Neurons, Hormones, and the Brain Chapter 4

Neurons, Hormones, and the Brain n n n n The central nervous system The peripheral nervous system Communication in the nervous system Neurotransmitters Mapping the brain A walk through the brain The two hemispheres of the brain Where is the self? Are there “his” and “hers” brains?

The Central Nervous System n n Brain Spinal cord n n A collection of neurons and supportive tissue running from the base of the brain down the center of the back. Protected by spinal column.

The Withdrawal Reflex

Peripheral Nervous System n Somatic n n Includes the nerves that are connected to sensory receptors and skeletal muscles. Autonomic n n The sympathetic nervous system mobilizes bodily resources and increases the output of energy during emotion and stress. The parasympathetic nervous system operates during relaxed states and that conserves energy.

Organization of the Nervous System

Communication in the Nervous System n The structure of the neuron n n How neurons communicate n n Different kinds of neurons Action potential Chemical messengers in the nervous system n Neurotransmitters n Major neurotransmitters n Endorphins n n Endocrine system Hormones

Structure of a Neuron n Dendrites n n Cell body n n receive information from other neurons and transmit towards the cell body. keeps the neuron alive and determines whether it will fire. Axon n extending fibre that conducts impulses away from the cell body and transmits to other cells.

Structure of a Neuron n Myelin Sheath n Fatty insulation that may surround the axon of a neuron.

Different Kinds of Neurons

Neurons in the News n n Canadian research has provided evidence for neurogenesis: the production of new neurons from immature stem cells. Stem cells are immature cells that renew themselves and have the potential to develop into mature cells; given encouraging environments, stem cells from early embryos can develop into any cell type.

How Neurons Communicate n n n Axon terminals release neurotransmitter. Neurotransmitter enters synaptic gap. Neurotransmitter binds to receptors that it fits.

Action Potential n A brief change in electrical voltage which occurs between the inside and outside of an axon when a neuron is stimulated. It produces an electrical impulse.

Neurotransmitter n A chemical substance that is released by a transmitting neuron at the synapse and that alters the activity of a receiving neuron.

Major Neurotransmitters n n n n Serotonin Dopamine Acetylcholine (ACh) Norepinephrine Gamma amino butryic acid (GABA) Glutamate Endorphins

Opioids and Substance P

The Endocrine System n n Endocrine glands release hormones into the bloodstream. Hormones regulate growth, metabolism, sexual development and behaviour, and other functions.

Hormones: Long Distance Messengers n n n Melatonin Adrenal Hormones n Cortisol, epinephrine, and norepinephrine. Sex Hormones n Androgens, estrogens, and progesterone.

Mapping the Brain n n Lesion method Electroencephalogram (EEG) Transcranial magnetic stimulation (TMS) Positron-Emission tomography (PET) Magnetic resonance imaging (MRI)

Mapping the Brain n Lesioning n n Involves damaging and removing sections of brain in animals, then observing their effects. Transcranial magnetic stimulated (TMS) n n Stimulates brain cells using a powerful magnetic field produced by a wire coil placed on the head. Can be used to temporarily inactivate neural circuits.

Electroencephalogram (EEG) n A recording of neural activity detected by electrodes.

Positron Emission Tomography (PET) n n A method for analyzing biochemical activity in the brain, using injections of a glucose-like substance containing a radioactive element. Active areas have increased blood flow. Sensors detect radioactivity. Different tasks show distinct activity patterns.

Magnetic Resonance Imaging (MRI) n n n Method for studying body and brain tissue. Magnetic fields align certain ions and compounds. When field is removed, these molecules release energy as radio waves. Computer calculates tissue density from radio waves. Provides clear, 3 D images.

A Walk Through the Brain n n n The brain stem The cerebellum The thalamus The hypothalamus and the pituitary gland The amygdala The hippocampus The cerebrum and lobes of the cerebral cortex

The Brain Stem n Pons n n Medulla n n involved in sleeping, waking and dreaming. responsible for certain automatic functions such as breathing and heart rate. Reticular activating system (or formation) n arouses cortex and screens incoming information.

The Cerebellum n n n Regulates movement and balance. Involved in remembering simple skills and acquired reflexes. Plays a part in analyzing sensory information, solving problems and understanding words.

The Thalamus n n Relays sensory messages to the cerebral cortex. Includes all sensory messages except those from olfactory bulb.

Hypothalamus and Pituitary Gland n n n Involved in emotions and drives vital to survival including fear, hunger, thirst, and reproduction. Also regulates autonomic nervous system. Pituitary Gland The pituitary gland is a small endocrine gland which releases hormones and regulates other endocrine glands.

The Amygdala n n Responsible for arousal and regulation of emotion and the initial emotional response to sensory information. Plays important role in mediating anxiety and depression.

The Hippocampus n n n Responsible for the storage of new information in memory. Compares information with what the brain has come to expect about the world. “Gateway to memory” because it enables us to navigate through the environment.

The Cerebrum n n Largest brain structure. Consists of upper part of brain and divided into two cerebral hemispheres which are connected by the corpus callosum. In charge of most sensory, motor and cognitive processes. Surrounded by cerebral cortex, a collection of several thin layers of cells (gray matter).

Lobes of the Cerebral Cortex n Occipital lobes n n Parietal lobes n n Somatosensory cortex. Temporal lobes n n n Visual cortex. Memory, perception, emotion and auditory cortex. Left lobe, Wernicke’s area. Frontal lobes n n Emotion, planning, creative thinking and motor cortex. Left lobe, Broca’s area.

Lobes of the Cerebral Cortex

Phineas Gage n n Gage was a railroad construction foreman An 1848 explosion forced a steel tamping rod through his head Others said he was “…no longer Gage…” Lost his job, worked as a sideshow exhibit

The Corpus Callosum n n n Millions of myelinated axons connecting the brain’s hemispheres. Provides a pathway for communication between the hemispheres. If surgically severed for treatment of epilepsy, hemispheres cannot communicate directly.

Split-Brain Experiment

Split-Brain Experiment n n n Subjects were presented information to one or the other side of their brains. Patients identified verbally the pictures to the right (i. e. , boy). When asked to point to the face seen, the patients pointed to the left picture.

Where Is the Self? n n n Most scientists assume that we call “mind, ” “consciousness, ” self-awareness, ” or “subjective experience” can be explained in physical terms as a product of the brain. Some contend that the brain consists of independent modules and that the self is an illusion. No one understands yet how subjective experience is linked to physical processes in the brain.

Are There “His” and “Hers” Brains? n n n After analyzing 49 studies of sex differences in brain anatomy, Canadian researchers found small differences between the two groups and larger differences within groups. There does appear to be sex differences in lateralization of language. Males show left hemisphere activation only. Females, left and right. There also appears to be differences in amounts of grey matter. Females have more.

3 Ways to Interpret These Findings n n n These supposed differences are stereotypes. A biological difference does not necessarily have implications for behaviour or performance. Sex differences in the brain could be the result rather than the cause of behavioural differences.